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Horst Miracle Probe Sensors for RV Black Water Tanks - Qty 4

Horst Miracle Probe Sensors for RV Black Water Tanks - Qty 4

Item # T21301VP
Our Price: $33.70
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Shipping Weight: 0.12 lbs
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Get an accurate reading of waste levels in your RV's black-water tank. Extra-long sensors are surrounded by Teflon to prevent false probe contact and incorrect sensor readings. Fits 3/8" diameter holes. Connects to existing wiring. Great Prices for the best smart rv from Valterra. Horst Miracle Probe Sensors for RV Black Water Tanks - Qty 4 part number T21301VP can be ordered online at or call 1-800-940-8924 for expert service.
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Valterra Smart RV - T21301VP

  • Monitoring System
  • Water Tanks
  • No Display
  • Valterra

Get an accurate reading of waste levels in your RV's black-water tank. Extra-long sensors are surrounded by Teflon to prevent false probe contact and incorrect sensor readings. Fits 3/8" diameter holes. Connects to existing wiring.


  • Provides an accurate indication of waste levels in your RV's black-water tank
  • Prevents false probe contact and incorrect sensor readings
    • Delrin body and Teflon tube surround sensor to prevent liquid residue or sludge from sticking to sensor
    • Considerably longer than standard probes to prevent false readings from buildup on sides of tank
  • Easy to install - fits 3/8" diameter holes
    • Use existing holes or drill new holes next to existing probes
  • Designed for RVs built to RVIA, CSA, and IAPMO standards
  • Connects to existing wiring and monitors
  • Quantity: 4 probes

How Miracle Probes Work

The monitor for your RV's black water tank shows a full reading when electricity is flowing between the tank's sensors. This circuit of electricity is completed when there is water or sludge in your tanks. If your empty tank is showing a full reading, that means water and sludge has built up on the sensors or the sides of the tank. This buildup completes the electrical circuit to give you a false reading.

Teflon Tube on Horst Miracle Probe

Unlike other sensors, which are prone to false readings due to buildup, Miracle Probes are surrounded by Teflon. The Teflon covers each Miracle Probe like a roof, helping to prevent liquid residue or toilet paper from building up on the probe. In addition, Teflon is not a conductive material and sludge cannot stick to Teflon. Miracle Probes are also longer than standard sensors, which prevents the probes from making contact with sludge that builds up on the sides of the tank.

Because sludge cannot build up on the Miracle Probes, a complete electrical circuit is only made when your tank is full and the water or sludge in the tank makes contact with the copper tips of the probes. This means that you'll only see a full tank reading on your monitor when your tank actually needs to be emptied.


The probes easily install into your RV black water tank's existing 3/8" diameter holes. You can also drill new holes next to the existing holes.

First, remove the existing sensors from the holes in your black water tank and replace them with the Miracle Probes. Once you have pushed the Miracle Probes into the holes, tighten the nut on each probe to create a leakproof seal. Then connect existing wiring to the new probes.

Once installed, rotate the exterior stud so that the milled flat section of the stud is aiming down and the Teflon roof is covering the copper tip of the probe.

T21301VP Valterra Horst Miracle Probes for Motorhome Black Water Holding Tanks - Qty 4

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Customer Satisfaction Score:

Customer Reviews

Horst Miracle Probe Sensors for RV Black Water Tanks - Qty 4 - T21301VP

Average Customer Rating:  4.7 out of 5 stars   (93 Customer Reviews)

Get an accurate reading of waste levels in your RV's black-water tank. Extra-long sensors are surrounded by Teflon to prevent false probe contact and incorrect sensor readings. Fits 3/8" diameter holes. Connects to existing wiring.


I have not installed these yet, but I will be very soon! I am replacing my cracked, black tank, dump valves,and these new style of sensors with a hood inside to cover the probe, and ensure accurate level reading! I'm also installing a brand new, majorly upgraded toilet, at least compared to the plastic, super short thing that was installed in 1988!! It's gonna be great to have all systems go, and a normal height toilet! No more falling backwards to sit! ?? Thanks again etrailer!!! You guys ROCK!!!


I got them a few days ago and today I installed them with little or no trouble. When I finished the tank level display showed empty. So I filled the tank with water to test them, and so far they are working well. After filling and emptying the tank the level indication returned to empty.



They are still working fine I am very satisfied with this product.


i installed them in the black and grey tanks. installation is easy if you can access the old ones. they seem to be very accurate.


Wonderful product. Soooo easy to install (drill new hole, insert probe correctly oriented and gently tighten seal jam nut, transfer electrical wire and secure - DONE) I have had no reoccurrence of error readings. Highly recommended. Excellent on time delivery. I am so pleased with this product.



I am getting 12 and 34 readings when empty. I will do a good tank flush and rotary spray and I am sure it will all be good.


The black tank sensors were very easy to install. My old sensors are spin welded so I had to drill new holes. There were no instructions included but are available on the net. If manufacturers would pay attention to the fine print, "place the bottom - sensor 8" to 13" away from the others." we wouldn't have so much trouble with the readout.



The new tank sensors make the KIP unite work right when mounted in the tanks 8 inches away from the bottom sensor.


I installed these on both black and gray water tanks in our 1995 Itasca "Sunrise". Installation was straight forward with no unexpected issues or obstacles. They have functioned as advertised and provide much improved level readings for the tanks. I would note that I take time to rinse and flush the tanks after dumping and use a down the toilet spray wand for better cleaning.


Came quick and easy to install. Took me about15 minutes to take the old one out and put the new ones in.



They have been working great with no problems. They were easy to install.


I replaced and old set of horst probes thinking that they may not have been the new improved ones with the guard around the probe. My first set ( factory installed ) worked well for a few months then became problematic. They did have the nylon guard(s), however, I replaced them anyway and have had the same results with the replacement ones. The sensor placement in the black tank from the manufacture could be a contributing factor as they are located at the end of the tank where it drains and not on the side where most manufactures place them. Mine are stacked directly over each other in a vertical line. Does not seem to be the best placement from what I have been able to research.


These were easy to install. Most RV tanks have 3/8 inch holes but the old ones can be real stubborn to remove. I remove the electrical cable, loosen, not remove, the nut closest to the washer, then use curved needle nose pliers to give some decent leverage, you may find the bulged rubber won't give without tearing the rubber (not the tank) or a portion might drop back inside the tank. They'll likely just flush out eventually but a 3/8 wood bit drilling new holes can work too. Then installing was simple just make sure the flat part on the threaded part is level so your probe shield is aligned to protect the probe.


Ordered latch and hinges (heavy) for Cargo trailer door and new tank sensors (very light and somewhat delicate) for our RV. Arrived in just a couple of days packed all in one perfect box with excellent packaging. Another site should take lessons from etrailer. Great price AND made in the USA!


Worked great, just installed them and now my black tank registers correctly. Took about an hour as I had to drill holes my original ones were the permanently installed type. I only installed the sensors for the 3 levels as the grounding sensor was in a spot that was too hard to access. This worked perfectly.


They appear to help some with false readings but still have to rinse the black and grey tank after each dump to clean the sensors. Have to fill the tanks up with fresh water and dump a second time to clean the sensors so they work properly.


Since replacing the sensors with the new Horst Probe I now can check the tanks and feel confident that the tank levels are correct and not worry about them over flowing. The best probe going. I highly recommend them for anyone with incorrect tank levels.


These sensors have a plastic hood that prevents the buildup of solids and tissure paper that produce false readings. These sensors don't provide as much data as something like the SeeLevel system, but for most casual full-hookup-to-full-hookup campers, they are plenty good enough.


Great product. Easy to install and they preform as advertised. Recommend them to any RV owner whose having trouble with their grey or black water level sensors


The service was great
Ordered the sensors
on good Friday, got them before noon on Monday I have had 11 motor homes starting in 1976 and never had a bad sensor until now. A 2 year old motorhome home only used a couple months each summer and all 8 0f the holding tank sensors were bad
They had deposits on the ends like calcium and they trapped material between the probe and the nylon top covering. Even the top ones that were seldom in any liquid had build up. I use chemicals and flush after each use.


I installed the probesin my black tank soon after I got them I found that I could not install them in the holes of the old ones so I plugged those holes with bolts and Silicone. The one's I purchased for the other tanks I haven't installed yet. I will install them before spring. I think the new probes are a little better but I still get wrong readings. It was difficult drilling holes because of the space around the tank


Après un an d’utilisation je suis très satisfait. Le lecture des niveaux est toujours exacte.
Bon achat!

[After a year of use I am very satisfied. Level readings are always accurate.
Great deal!]


No more 2nd guessing the black water levels.
probes perform as advertised and O haven't had a single false readout since installation.
Easy to install. My high, high probe was a little hard to.reaxh, but that was due to the trailer configuration, and not the probe design.


These are a great replacement for the factory sensors on our 10 yr old trailer. Sensor panel now has a chance to give a more accurate reading for the black tank. Easy to install.


Bought to replace the level sensors in black water tank on my motorhome. Three worked great but one came apart when tightening and a portion of it fail inside of the tank.


I installed these probes last year to replace the originals (20 years old) and they work great! Installation was straight forward and they came with good instructions.


I am thoroughly pleased with these extensions, the ones previously on my RV frequently leaked, causing problems these have performed with no issues since installed over a year ago.


Arrived in a timely manner and installation was easy, mine were the same size as replacement. Have not used the tanks yet, going camping labor day weekend to test them out.


For a while, this will just be a review of etrailer as the installation of these probes will be 'another day' since the belly cover of our Montana will need to at least partially come down and this is just not a good time.

etrailer has been great so far :-}

Show More Reviews

See what our Experts say about this Valterra Smart RV

  • Will The Horst Miracle Probe Sensors # T21301VP Fit Into 3/8" Threaded Holes on Valterra Water Tank?
    Yes, the Horst Miracle Probe Sensors # T21301VP will fit into the existing 3/8" threaded holes on your Valterra tanks. The probes will push into the holes and you will tighten the first nut to create a leakproof seal.
    view full answer...
  • Will The Horst Miracle Probe Sensor For RV Black Water Tanks Fit A 2001 Winnebago Journey MH?
    As long as your tank on your 2001 Winnebago Journey DL Motorhome has a 3/8" diameter hole opening, then the Horst Miracle Probe Sensors for RV Black Water Tanks # T21301VP will work great for you. You can either use the existing holes in your tank, or you can drill new holes next to the existing holes.
    view full answer...
  • Can Horst Mircale Probe Sensors BE Used On A Holding Tank With 1/2" To 5/8" Thick Walls
    The gasket on the Horst Miracle Probe Sensors for RV Black Water Tanks # T21301VP is only about 1/4" in length so installing it in something thicker could potentially allow waste water to leak back into the hole and possibly out from the gasket. That being said, you could also caulk around the gasket on the outside of the tank to prevent any leaks. The key is really just making sure that the sensor is in enough to actually touch the water. If it sits back inside the hole there's also the...
    view full answer...
    Image 1 for
  • Troubleshooting RV Water Level Sensor Not Showing Full
    You might have disturbed the wiring of the sensors when you cleaned them. When the sensor is grounded it will show the reading so if you ground your highest "full" sensor and it show that it's working that would mean you have a wiring issue with it.
    view full answer...
  • Do the Valterra Horst Miracle Probe Sensors Need to be Cleaned
    I spoke with my contact at Valterra regarding the Horst Miracle Probe Sensors # T21301VP referenced in your question. She stated that the probes do not require any kind of maintenance once installed and you will not need to clean them. Because the probes are surrounded by Teflon, they are not prone to liquid residue or debris buildup. She was not able to confirm an exact lifespan for the probes, however she did state that they are designed to last and there is no reason that they would...
    view full answer...
  • Miracle Probe Sensors Work With Aladdin Black Water System
    The Horst Miracle Probe Sensors # T21301VP are universal so they will work with your Aladdin black water setup in your coach.
    view full answer...
  • Replacing Black Water Tank Sensors
    You do not have to replace your sensors directly, but at the least you are going to want to install the Horst Miracle Probe Sensors # T21301VP next to your old sensors. They are positioned in a way that allows the reading to be as accurate as possible.
    view full answer...
  • Compatibility of Valterra Black Water Tank Sensors with Existing System
    The Horst Miracle Probe Sensors for RV Black Water Tanks - Qty 4 # T21301VP will work with an exiting system where the sensor is installed on the top. The probes easily install into your RV black water tank's existing 3/8" diameter holes or you can also drill new holes next to the existing holes. These sensors have a Teflon sleeve surround to prevent build up and give you a more accurate reading.
    view full answer...
  • Black Tank Sensors fro Aluminum Holding Tank
    The Horst Miracle Probe RV Black Water Tank Sensors # T21301VP can be used on your aluminum holding tank since they have a rubber grommet that isolates the probe from the tank. When you tighten the first nut on the probe the grommet expands to provide a secure leak-proof seal at the hole. This allows the probe to work fine on aluminum as well as plastic holding tanks.
    view full answer...
  • Troubleshooting Valterra Horst Black Water Tank Sensors Read Empty All the Time
    Most likely a ground wire issue. There is one common ground wire between all tank sensor packs and frame. Quick test is to jumper between the bottom sensor and good ground, should read empty if tank is empty. Then you can jumper from the bottom sensor to the one above it for 1/3 and the one above that for 2/3 and the top one for full. If that works then check for the common ground wire. We have added ground wires in addition to the original one.
    view full answer...
  • Troubleshooting Tank Water Sensors Reading Empty When the Tanks are Full
    When sensors like the Horst Miracle Probe Sensors # T21301VP are having improper readings of empty even when full, it is more often than not the result of a ground issue. The sensors will only read full when the tanks are full, completing the electrical circuit. If the ground is bad the circuit can not be completed and the sensors will not work. I understand that you were careful not to disturb the wiring other than the sensor you were working on at the time. Unfortunately the nature of...
    view full answer...
  • How Far Apart Should the Horst Miracle Probe Sensors be Installed
    I spoke with my contact at Valterra for confirmation of the proper way to install the Horst Miracle Probe Sensors, part # T21301VP. They do not have tests on the maximum distance possible between the sensors, but stated they will work properly if they are installed using your RV black water tank's existing 3/8" diameter holes (by removing the existing sensors from the holes already in your black water tank). If that is not possible, then drilling holes right next to those holes will work...
    view full answer...
  • Will the Horst Miracle Probe Sensors item # T21301VP Work w/ a Fiberglass Tank?
    Yes, they will. The Horst Miracle Probe Sensors item # T21301VP will install in your fiberglass tanks existing sensors holes. The water and waste in your black tank will touch the exposed probe on the bottom side of the sensors. This will create a circuit that will indicate a full tank. The Horst Miracle Probe Sensors item # T21301VP are covered in Teflon to repel any waste or toilet paper from attaching to them giving you a false full tank reading. These install into existing 3/8" diameter...
    view full answer...
  • How Many Sensors Does RV Have For RV Black Water Tank
    It should only have 4 sensors. That is the standard amount found on most RVs which is what the Horst Miracle Probe Sensors for RV Black Water Tanks # T21301VP is designed for.
    view full answer...
  • Horst Miracle Probes for Gray and Black Water Tanks
    For a Horst Probe for a black water tank you would want the part # T21301VP for a quantity of 4 or for a gray water tank you would need the part # T21302VP. The probes of these kits are straight and are not a knock-off. There was a design change though which helps prevent debris getting caught in the tank. If you check out the picture I attached you will see what was prone to happen with old design.
    view full answer...
    Image 1 for Image 2 for
  • Can Valterra Horst Miracle Probe Sensors for Black Water Tank be Used in Gray Water Tank
    I spoke with my contact at Valterra regarding the Horst Miracle Probe Sensors for Black Water Tanks # T21301VP referenced in your question. She stated that there is no reason you could not use a couple of the black water probes in your gray water tank. The primary difference between these and the Gray Water Probes # T21302VP is that the black water probes feature an extra coating/seal to protect them from debris. These sensors will work great in your tanks to provide an accurate indication...
    view full answer...
  • Grey And Black Water Tank Sensor Recommendation For A 2013 Jayco Eagle Premier 5th Wheel
    For your 2013 Jayco Eagle Premier 5th Wheel, I recommend checking out the: -Horst Miracle Probe Sensors for RV Black Water Tanks # T21301VP for your black water tank, and, -Horst Miracle Probe Sensors for RV Gray Water Tanks # T21302VP for your grey water tank. These sensors will fit into 3/8" diameter holes, and will work in place of existing holes or you can drill new holes next to the original holes.
    view full answer...
  • Can the Horst Miracle Probe Sensors be Used with an Aluminum Tank
    I spoke with my contact at Valterra. The Horst Miracle Probe Sensors, part # T21301VP, should not be used with any metal tank. The metal will interfere with the readings, rendering them inaccurate.
    view full answer...
  • Why Would Blank Tank Full Sensors Give False Full Reading When Sensors are New
    When RV holding tank sensors incorrectly read full, it is typically due to residue. Since your trailer sat for a while it's very likely there is residue of some kind on the sensors. The best way to keep your tanks sensors working correctly is to take proper care of the tank itself. The waste tanks are more prone to sensor issues, simply because of the nature of the materials contained than fresh water tanks. What you need is a tank cleaner like the part # CAM41146 to break up everything...
    view full answer...
  • Troubleshooting Black Water Tank Sensors Giving False Readings
    We haven't received a lot of customer feedback regarding the Valterra Sensor Power Sensor Cleaner # V22011 that you referenced so I can't really provide an accurate success rate. The treatment is specifically designed to clean the sensors in an RV's black water tank to help correct those incorrect readings you keep getting but to be honest for how long you've been dealing with this issue along with the fact that you already tried cleaning them without success it might just be time to replace...
    view full answer...
  • Wand For Cleaning RV Black Tank With Sensors Which Are Reading Incorrectly
    It sounds like you either have a Sensor # T21301VP that has gone bad or more likely there is some debris stuck on the sensor that is making it think it is full. I recommend taking a Valterra Spinning Master Blaster Tank Wand # VAL88VJ and using it to clean out your black tank. This wand has a spinning tip that allows it to spray water all around the tank and can help to clear debris stuck on the sensors and walls of your tank.
    view full answer...
  • Maintenance of Horst Miracles Probe Sensors for RV Black Water Tanks
    It sounds like the probes on your Horst Miracle Probe Sensors for RV Black Water Tanks, # T21301VP have been introduced to something that has caused damage to them. Possibly from a harsh chemical cleaner that ate away at the plating. You may need to consider replacing them. I have included a couple of help articles that we have posted on the site that walk you through the steps of cleaning and maintaining a waste tank. The Valterra Sensor Power Sensor Cleaner, # V22011 is my recommendation...
    view full answer...
  • Recommended Black, Gray Water, and Fresh Potable Water Sensors for Level Monitoring System
    We do not have any monitoring system for your water levels. We do however carry the sensors for the tanks that will connect to those monitoring systems. You can make your own system without a monitor with a simple light connected to a battery. You would simply connect power to the lowest level sensor an then mount a sensor at the desired level or levels and connect the positive wire of the light to the sensor and the ground of the light to any grounded metal surface. I recommend using...
    view full answer...
  • Adapter Needed To Go From 7-Pole Blade To 7-Pole Round Pin Connector
    If your 2015 Ford F-250 has a standard 7-way then you can use an adapter like the Pollak Trailer Connector Adapter - 7-Blade Plug to 7-Pole Round Pin # PK12727 to go from the standard 7-pole blade to 7-pole round pin connection type. If you only had a 4-pole connector then you could use the Custer Trailer Connector Adapter - 4-Way Flat to 7-Way Round # KIT-7P-4 instead.
    view full answer...

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