The "calling" for water pressure is interesting, if we assume there is a leak filling the tank.
A leaky faucet does not call for water. The pressure would constantly be calling, and there would be no difference that would call for it.
A residential toilet can call for water. A leaking bowl seal would drain the bowl, lower the tank level, call for more water to fill the tank. Most RV toilets do not...you have to flush. Plus this would assume that your toilet is flushing into the gray tank...yuck.
A water heater can also call for water, but that leaves a draining/gray water tank filling question????
My pressure release valve on the water tank would just spew water on the access panel. Is it possible yours has a drain into the gray tank. Pressure builds, drains into tank, calls for water to fill tank....repeat. That is still a lot of filling/draining to fill a gray tank.
What about a fridge with ice maker/or water dispenser. A leaky dispenser is probably like a faucet, which would be a constant leak---constant pressure. The ice maker would call for water...I have no idea where they would drain to???? .
Perplexing question. You MUST post the answer when you figure it out.
