If water is leaking onto the floor of your shower or onto the base of your Thetford cassette in a dual toilet shower setup the water level tubes are leaking. The original product used to seal the white tubing that allows water to travel to the sight tube has broken down with age and allows the water to leak out. We use a sealant to fix the leaks with the front tube relatively easy to get to. The rear tube is as its at arms length and very hard to get to so I suggest using an epoxy resin or fibreglass product to rectify this problem. Silicon will not work, latex spray is too soft & thin to hold back the leak and urethane just isnt strong enough to hold back the weight of the water pressure.
Hoping this information helps caravaners avoid unnecessary repair costs when their repairers cannot find the problem.