Sequence to use to clean up "black water tank",please.

There are products available from Camping World from there retail locations or from there online store. If this has not been done on a regular basis you might need to do the job more than once. In extreme cases I have heard stories about using these products but not filling the black tank completely and hooking up the tow vehicle and going for a ride. The sloshing in the black tank will help to break things loose--Good luck!!!!!