Replaced toilet won't sit on floor

[Howie3]

I am in the process of replacing my old Thetford toilet with a new Thetford, however when I insert the rubber ring provided, the base will not sit firmly on the floor, even when applying weight. I realize that it is meant to be held down by the bolts and that a bit of flex is necessary for a proper seal, however it sits quite high and I am afraid that if I tighten the bolts too much, it will crack the base. My neighbor who is a plumber suggested I use a wax ring instead but just curious why a toilet from the same manufacturer would not fit on the same flange (it does sit flat without the ring in place). Anyone else experience this or have suggestions? I do not want to replace the flange as it has the right depth of pipe to screw into the black tank whereas the new one at the RV shop I would need to customize to fit into the tank.

[Howie3]

Mission accomplished. The rubber ring eventually settled as I alternated tightening each bolt without too much pressure. I previously replaced the water intake line to the toilet so hooked everything up and pressurized the lines with the water pump on. No leaks after my handiwork and two winters of inactivity!
Will reassemble the tub and surround tomorrow, then replace the vinyl floor that split over the winter.
Will feel like a new trailer when done.
Howie

[Howie3]

newman fulltimer wrote:
If its off by a half inch the seal will compress once you tighten it down

I’ll try that tonight. Bought a $2 wax ring just in case.

Thanks to all for your advice/suggestions. RVing is fun but the repairs not so much. Truly appreciate this forum with my limited DIY abilities.

Howie

[newman_fulltime]

If its off by a half inch the seal will compress once you tighten it down

[Howie3]

old guy wrote:
home depot sells wedges to keep the toilet from rocking and the seal should be working to keep water and smell out of the room

Thanks for the suggestion. I think I would rather have the base flush against the floor (no pun intended!) and the wax ring being more pliable should work. Just wondering why there would be a height difference between two seemingly identical toilets by the same brand.

[Howie3]

bdpreece wrote:
Have you physically compared the two toilet bases?

Wish I could. I removed the old toilet last year and went out on a dump run.

[old_guy]

home depot sells wedges to keep the toilet from rocking and the seal should be working to keep water and smell out of the room

[bdpreece]

Have you physically compared the two toilet bases?

[Howie3]

The old ring is a slightly different shape but otherwise about the same thickness. It is in decent shape and fits on the base of the new toilet so I thought about using it instead. However, same problem of being too high off the floor. I'm kinda puzzled.

Howie

[bdpreece]

No real answer but a question. When you removed the old toilet did it have a thinner rubber ring than the new one? Is it the same model toilet? Different model toilets may have different installation specs. If you can't find a thinner ring or you can't trim this one down a wax ring may be your only option.