thetford cassette c-200cs?

www.thetford-europe.com

go to service then click repair instructions download repair pdf it covers all models and any other pdf takes your fancy. Just took a look and it has its own pump so follow below it may just be stuck, or fuse. Yes you will get other water that comes from a different source.

Meanwhile carry out current test.
turn on a 12 volt light in the toilet cubicle press flush if light dims current is reaching the pump. So pump is either knackered or jammed with lime from siting in water and inaction for long period. If no current at pump look out for the fuse.

Always drain off the toilet water tank if leaving in store for a long period leave a note to tell you to re-fill.

bob
August 2013