Motorhome flush leak

Drain downs for flush tanks are usually external to the van as is the top up point. Are you sure the bung belongs to the flush tank, they are usually on the end of a glass tube. If it so you have an unusual installation!

peedee

The drain down pipe on thetford toilet flush tanks seem shorter than in the past ,,i make sure when emptying i hold the pipe as clear as possible  away from LV ,on the list of to dos is to make the pipe longer, as it could well be the source of the "leak"

Thetford toilet models have changed over the years and also vary between motorhomes. It would help if you can tell us the toilet model and its age and the make/model of MH.

It may be as simple as you have overfilled the flush tank.When we changed to our current 2019 Warwick Duo I had "the horrors" when I found pink flush liquid on the shower floor.Never had the problem with out two previous  MHs.After speaking to the Service Dept.at our dealership they pointed me to a bit in the Thetford toilet instructions which advised travelling with no more than half a tank of flush.I followed this advice and no more wet shower tray.Been at this game 33 years and still can learn something new.😳.