[rohrmann]

I am wondering if the hammering is actually coming from the flush valve on the toilet, seeing as that is the only thing that causes the hammering. We replaced our Thetford toilet a few years ago with a Dometic 310, which has worked great. The only glitch we had was several months ago, when it stopped flushing, and I discovered the flush valve had backed out of the housing that holds it in place. After closer checking, I discovered that the replacement valve comes with a couple self threading screws to hold it in place, along with the plastic clips. I installed a couple of screws, and all is good. All this to say, we had the hammering just prior to the valve coming loose from it's clips, so maybe your valve is the problem.