Your system is set up wrong. The Pursan system grinds and basically shocks the waste - killing about 99% of the bacteria. That treated waste is then OK to directly discharge overboard IF you are in an area that allows it. To take treated waste from a Purasan system and store it in a holding tank is 100% wrong. The 1% of bacteria that is left will grow in the holding tanks. It is anaerobic bacteria - that is what causes the smell.

So, your system is plumbed wrong. Since it it plumbed wrong, it has probably been used wrong. I have no doubt that the previous owner flushed chemicals down the toilet. Those chemicals probably killed the plates in the Purasan system.

Here is what you need to do. First find out if where your boat is docked allows the treated waste from the Purasan to be discharged directly overboard. If so, then you can retain the Purasans and plumb them for direct discharge. You will need to verify that your Purasan systems still operate correctly - as I said earlier, the plates in the system are probably fried. Also, be aware that the discharge - while odor and bacteria free - is not necessarily clear. Depending what you are disposing of, it can be anywhere from slightly discolored to brown. If you cannot discharge directly overboard, then you need to rip out or bypass the Purasan systems and go directly from your toilets to the holding tanks. If you use the system correctly, it will not smell.

Vic Willman did retire. And, he was an extremely nice and helpful guy.

Also, if you do have a filter on your vent line, it was ruined when it got wet and must be replaced.