I have a Tiffin 2018 Allegro Bus 40 AP with a Dometic Concerta 4100 series toilet. The bowl no longer holds water; was in Red Bay, AL and had the seal replaced, then re-adjusted number of times. Sti...
I can't find that model toilet, but, assuming the seal is round and fits over a sliding flap, try pushing down on it all around its circumference - but not hard enough to remove it.
I stumbled on this fix when trying to replace my seal. I pushed pretty hard but it would not come out, but, voila, now my toilet holds water.