Originally Posted by CrawfordGene
If there were no outlet from the black tank, the tank would expand and that can cause lots of trouble and that has been reported on another thread. If the soil stack is blocked—say from a bird's nest built while the trailer is stored—you could have a problem. Someone had the floor pop up and some supports bend.
Now it comes back to me, or did when I was filling my fresh water tank. Someone overfilled their fresh water tank, the floor popped up and I think tank supports were bent. If you jam a hose in the inlet so overflow can't get out, and the relief hole is blocked, that could happen.
That's a reason for the adapter that fits on the end of a hose and goes into the tank so you don't have to stand there holding the hose or jam it in.
With the black tank (and grey too) if their soil stack was blocked, the same thing could happen, but it might take a condor's nest to be heavy enough to hold back the water pressure.
Thought to ponder: if we have black and grey tanks, what color is the fresh water tank? The water that comes out of the grey tank is not grey, but kind of soapy colored, so shouldn't it be the cream tank?