My HB is a pontoon style boat with a 70 gallon black water tank located under the flooring and midship on the 66' vessel. I have 2 toilets plumbed with 1.25" wastetank hose going to the holding tank with probably 5' - 7' runs each. The pump out line is hard plumbed with a thick PVC pipe exiting the tank and going to the stern of the boat. There's also a vent tube that's probably 1/2" that exits the tank and goes inside the boat's port wall and vents 1/2 way up the side of the port.

I have tried 3 different waste treatment chemicals on this boat, but none of them have really worked well. My neighbors at the dock are starting to regularily tell me that my boat stinks. The problem is at its worst whenever someone flushes a toilet. It'll clear the dock!

After talking to the boat's manufacturer, I know it doesn't have a filter in the vent tube, but I'm not certain I could even install one now if I wanted to because I don't have access to the tube. If I install one, it needs to be well above the waste tank so it doesn't get saturated when the holding tank is overfilled. How effective are these filters?

What can I do to improve this situation?