Black tank overflow

dshinnick wrote:
So, it would seem we have two mysteries: why is the fresh water tank filling to overflowing with the valve in the City Water position, and why is the black tank filling to overflowing and backing up into the toilet?

Anybody near Asheville, NC, want to come over and join in the fun?

:0)

1. The City Water valve is seeping and not shutting off for your water tank fill problem
2. There are only 2 things going into the Black Tank. (1). The toilet. (2). The black flush. VERY FEW Motorhomes have the Washer or the Lavy Sink plumbed to the Black tank.
3. As you found out and hopefully have disconnected, Having either a Y water hose connection or using the water Bay water faucet with a hose connected to the Black FLUSH input is NEVER a good idea. I advise customers that want to do that to install a minimum of 2 in line water valve shut offs to prevent a shut off from seeping and then filling the tank.
4. IF you are positive the Toilet is not leaking water down and you have the Black water input hose connection NOT connected to anything, then I would suspect a previous owner has done some type of modification to the Flush piping. Some owners and I have done this for a flushing problem, have installed a fitting in the 3 inch down tube between the toilet and the top of the tank. connected to a valve by the toilet so when you flush the toilet, you open this valve only while flushing to help slide the debris into the tank. This modification is ONLY done when the down pipe has a few bends instead of a straight pipe into the top of the tank. Maybe a previous owner had this type system installed? Doug

Forgot. NOT very common, but your water Pump valve could also seep. But that is easy to check. You remove the entry side water line when connected to City Water. You will know if it is leaking backwards.