[JRTJH]

There is another issue with equalizing the gray and black tanks that's not yet been brought up. Most Keystone RV's are built with 3" black tank valves and 1.5" gray tank valves. Attempting to equalize would be "large solid chunks" in the 3" line and "migrating them to the 1.5" gray tank line with little or no water pressure. Chances are very good that the solids would get stuck in the smaller line and/or valve. That might be "OK" for a lucky one time event, but doing it on a regular basis, I'm guessing someone is going to be "digging poop out of the gray tank" before the end of summer.

I wouldn't recommend equalizing gray and black tanks for many obvious reasons such as smell through the vent stacks, possible leaking HEPVO valves (smell in the shower) and the inability to rinse the gray tanks (no flush valves) but also, maybe even more important, the much smaller size of the discharge plumbing. It's hard to push something designed to flow in a 3" valve through a 1.5" one.....

IMHO, that's just asking for trouble and expensive repairs.