Replacing SeaLand 3110 Toilet With Dometic 420 Using a 4-Bolt to 2-Bolt Adapter

Updated 09/16/2026 | Published 09/09/2026

Products Featured in This Question

Dometic RV Toilet Floor Flange Adapter Kit - 4 Bolt Flange to 2 Bolt Toilet - White

(21)

$115.16

Dometic 420 RV Toilet - Standard Height - Elongated Bowl - White Porcelain

(6)

$458.99

Question:

I have to replace my Dometic/Sealannd 3110 toilet in my 2008 Monaco Dynasty because the circuit board is going out and is undependable. I want to replace it with a Dometic 420, but the floor flange is a 4 bolt, and I need to adapt it to the 2 bolt mount. The 3110 did not mount to the flange, if you are familiar, the neck of the toilet ped into an extension bolted on top of the floor flange, and it is held down by 4 lag bolts into the floor.. One of the biggest issues is the footprint that the 3110 had, and I understand that Dometic. has a decorative plate with a 4bolt to 2bolt adapter. 559269-0890

asked by: Bill D

Expert Reply:

Thanks for letting us help Bill. It sounds like the Dometic RV Toilet Floor Flange Adapter Kit - 4-Bolt Flange to 2-Bolt Toilet # DOM73FR is exactly what you need. This kit allows you to adapt your existing 4-bolt floor flange to the 2-bolt mounting pattern used by toilets like the Dometic 420 RV Toilet # DMC67JF. The included adapter base also provides a finished mounting surface that will help cover the larger footprint left behind by your existing SeaLand 3110, so you won't be left with the old mounting area exposed.

I'm going to attach a photo of the instructions to give you an idea of what to expect during the install.

Are you planning any other upgrades to your Monaco Dynasty?

expert reply by: Christopher H

DOM73FR Instructions
(click to enlarge)

Bill D.

9/15/2026

This worked perfectly. Recommend this conversion to anyone with the D/S 3110 that has a bad circuit board. The adapter and plate completely covered the base area of the 3110.

Christopher H.

9/16/2026

@BillD This is very helpful. Appreciate you hopping in here! Did you replace your 3110 with the Dometic 420 as well?

Bill D.

9/16/2026

@ChristopherH yes, Dometic 420 on top of the adapter. The D/S 3110 had a collar on top of the four bolt flange in the floor, simply remove that collar install the two bolt adapter on top of the four bolt floor flange, which gave room underneath the 420 base for the plate to cover up the old base footprint from the D/S 3110. The base of the D420 tightened down perfectly to hold the bass plate in place and secured the toilet at the same time. The bone colored base plate tied in perfectly with our earth tone bathroom. I’ve got a picture, but don’t know how to post it here.

Christopher H.

9/16/2026

@BillD Yeah sorry we aren't able to receive photos in the comments. If you wouldn't mind forwarding it to [email protected] I'd like to take a look. Really appreciate all the detail here! This will be very helpful for anyone looking to tackle the same project.