That was made for my B323 , 2006, water tank. I never tried it on the holding tank, but they look the same. At a seminar by the local Benny dealer, I asked about a tool for this purpose. He said he knew of none. Necessity being the mother of invention, you know. I'll try to remember to try it on the HT tomorrow. Yes, make it so you can use two hands on it. There are BIG rubber o rings on those fitting, and hard to break loose.... does your wrench also fit the water tanks bungs ...?