Basic RV water system.......
Except on your MH bathroom sink drains to black tank vs grey tank
SOoooooo.
Only 2 ways water is getting into your black tank
THE BATHROOM FAUCET or THE TOILET
Problem is not the pump. It is doing what it is designed to do. Pump water on demand. Demand is either an open faucet (shower, sink, toilet etc.) OR a leak. Leak would not go into the waste tank.
Bet you travel with toilet lid closed and therefore don't notice the water running. BUT you should be able to HEAR the pump running cause none of them are that quiet.
