Yep, 7am and I'm thinking about the holding tank. Actually I have been meaning to post this for some time and keep getting distracted.

OK, so on all the sailboats we always used the same holding tank chems available from the local marine supply. Tanks were all in the 15-18 gallon range, every pumpout got a fresh 8oz bottle of the blue stuff down the head. No problems with odor.

With this boat, same deal, same chems, same procedure but wow!!! Pumpouts are quite a different scenario, the smell about knocks you off the dock. I have been trying to figure out what the difference is, as I said, chems are the same and I'm pretty sure the other stuff that goes into the holding tank has not changed chemically, the only thing I can figure out that is different is the tank location. On the sailboats all the tanks were against a nice cool hull, in this boat the tank is in the engine room. Is it possible that being in a nice warm environment like that makes the chemicals less effective?

We don't add cleaning chemicals to the head or anything like that so I don't think there is any neutralizing reaction going on. When we took delivery, the tank was about 1/3 full and whatever was in there was in there for 2-3 years. That pumout was also pretty painful on the dock. End of the season ritual is a pumpout, flush twice with fresh water, then two gallons of the pink stuff pumped in through the head.

Any thoughts on my theory?