Thetford toilet and the water leaks down pretty quickly. I am thinking it’s the blade seal and I guess that means removing the toilet to do the job. If thats the case, I am tempted to pay someon...
When ours starts not holding water, we usually have to clean mineral and lime deposits off the seal, and then it works fine. Ours is 19 yrs old and still doing good. We use some Lime Away in a little water and let it sit there for about half hour, then use a toilet brush on the seal. Rinse toilet, put a little water back in and good to go.