[Camp CA]

I also fill and flush per the procedure as RMcNeal in post #9 using an in-line P3 turbine meter to fill with the quantities noted.

I will add my hoses (city water and flush) are connected to the trailer AND shore water supply with quick disconnects. That way, once I charge the black tank with 15 gallons BEFORE use, I will disconnect that hose until I am ready to flush the black tank out, as a safeguard to mitigate the risk of the shore water valve leaking (have had that happen) or someone turns it on and inadvertently, both of which will overfill the black tank and onto the trailer floor.