Originally Posted by rfstuart
The black water drain valve should be kept open anytime you are pushing water through the flush fitting. If you are trying to fill the black water tank with the flush and the grey water tank gauge shows an increase, you may have reversed wires at gauge like I did. They either installed flush in wrong tank or wired gauges backwards. Wire are a lot easier to fix. I just re read your post and if it shows that your shower is flowing into the black tank on gauges, the wires have to be reversed. The grey tank is directly below the shower.
When I bought my Challenger Thor could not tell me, initially, what fixtures were plumbed into which tanks. I have two 40 gallon grey tanks and one 40 gallon black. After ensuring all tanks were empty I started running water through each fixture (Kitchen sink, shower, etc...) what I found was that anything on the drivers side went into one grey tank and the fixtures on the passenger side went into the other. The toilet only went into the black. I later got the waste water diagram from Thor which confirmed what I found during testing. My black tank flush does in fact flush the black tank. My panel controls are wired to the correct tanks.
For piece of mind you may want to perform a similar test so you know for sure what is draining into what. There are some models that have the bathroom sink plumbed into the black tank instead of a grey tank.