I don't know which forum or topic I was reading but a fellow camper said he puts mineral oil in his black tank. The oil will oil the mechanics of the tank valve. I went to Home Depot and bought a 8oz bottle of butcher block oil which on the label indicated it is mineral oil. I think the idea is to have a very light and fine oil in the tank which will cover the valve components. After camping in Cordele, GA I emptied and cleaned out the black tank, then filled it approximately 1/3 full, I added the mineral oil and drove the camper 200 miles to Cartersville, GA. After the tank was full I emptied the tank and found the valve worked as if it was brand new. I have emptied the black tank now three times and the valve is still working great. Before adding the mineral oil, the dump handle was very hard to pull out and it didn't fell like the valve was entirely opening. I was waiting for the handle and valve mechanism to come apart. This mineral oil works for me!
