Jim, I have found our models tend to be a bit more odoriferous than most other ones. I believe a good part of it is we are only vented on the port side and cannot get any cross ventilation to the tank.
I have found several other issues that have contributed over the years:
Cracked inlet elbow from the forward and midship heads to the tank (curious if you have the crazy metal pipe arrangement at the through hull we have in the midship bilge). Replaced hose from through hull and metal elbow, T and nipples with PVC (this summer). We are fortunate that the tank pick up tube is PVC so we don't have to replace ours. As we have wood floors, it would have been a major headache to do that.
Hose permeation. In the last 2 years I have replaced all the discharge sanitation hoses. Inlet hoses were checked and did not need to be changes.
My third pump is at Raz ready for pickup. They have rebuilt all of them over the last 3 years so stators and seals are all fairly new. That said, I will be replacing the oldest stator when I pick up the pump. Stators apparently last 2-3 years. This one is nearing 3 years old.
Tank additives. I now use a combination of a bacterial additive and NuetralizerX. I won't say we never stink but we have to be close to 3/4 full before we worry about our neighbors getting irate. I put a half scoop of Neutralizer in our master head daily and it seems to keep it under control.
Not sure if you are raw or fresh water flush but that is probably the most sure fire way to keep smell down. Fresh water is not conducive to the bad bacteria that causes stink....
