Cleaning the black holding tank can be difficult, especially on motorhomes without a flushing system. I’ve found the best way to be certain our tank is clean is to visually verify it is empty.
To do this, I use a sturdy plastic cup I modified to hold the toilet valve open. I cut the bottom off the cup and drilled holes in the side just above the level where the valve is when the cup is placed to hold the valve open.
With the valve open, I then dump a bucket of water down the trap while connected to the RV park’s sewer connection. By using the cup to hold open the toilet valve, I can look through the opening to ensure the tank is clean (the toilet dumps directly into the black tank). This also allows me to dump a bucket of water directly down the toilet opening, which further helps flush the tank.
Don Callahan | Fairbanks, Alaska