How To Clean A Clogged Black Water Tank Drain
I learned this trick from an old time rv'er. It has worked everytime.
First thing I do is put a ladder up against the airstream and raise it high up. With both grey and black valves closed I disconnect the black hose
at the rv park septic drain dump. I raise the black tank hose as high as I can and attach it securely to the top of the ladder. Then I go back down and turn the water on and fill the black water hose up to the top. Turn hose hose off, pull back the black water tank valve and stand back. Water
will come down with alot of pressure and clear most cloggs. Immediately close the black water tank valve, reconnect the black water hose to the septic system, open black water valve again. Job done. Hasn't let me down yet.