Replacing a perfectly good Thetford toilet. Few reasons- Primary, original has hand valve at rear of toilet, Margarets having a hard time reaching back to flush. New one will be foot controlled...
"Push-Tite" by SiouxCheif- Fits 3" pipe ID, most RVs (4" pipe ID available). Probably other brands and likely sources. This came from Home Depot. While it wont make you squarer I know the extra (or less) 3" down & up of new toilet will be welcome by us :)
It seems to me these, on a toilet that sets on top of black tank is ideal.