Water Pump on Quantrum WS31
I drive a '16 Thor Windsport 31 S, which is probably very similar to your coach. There is a valve near the fresh water tank that allows you to drain the tank. In the same line, there is one that allows you to attach an air line to the system and blow out the faucets and lines, WITHOUT allowing the air pressure from entering the fresh water tank. The culprit valve is between the air input and the tank. At least that is the set up on my Windsport.