"Black" tank does not hold much and pressurizes

[Tennessee River Rat]

I had a similar problem with our last boat. We had overfilled our tank. It also had a charcoal filter on the vent line. Once your waste tank overfills the filter is toast. And it does pressurizes the system until you either replace or take filter off and connect some hose where filter was. Everything worked fine after that. But it will smell on the side where you vent exits. I started buying filters on amazon and much less $. I changed it out once a year and never had another problem.

[crquisto]

I have a 2000 406 with two holding tanks. Neither has a filter in the vent line and I don't think they ever had them. When I bought this boat, I soon found that every time I flushed either head we blew horrible odor out the vents. After searching this forum, I found Zaal No-Flex Digester to treat my systems. I didn't have a ton of sludge, but this product eliminated ALL odors after two treatments. I am not a Zaal salesman, but I will attest to its effectiveness.

[g36]

+1 on noflex been using this in my 405 for 4 years now

[CptBacardi]

Ok I got in there and got it fixed! I removed the filter, cut the hose shorter and attached it directly to the through hull. The through hull was not clogged, but the 90 degree elbow at the tank was. A clothes hanger made quick work of that and I definitely knew when the clogged released because the holding tank relieved a bunch of pressure. Now the tank seems to fill and pump out correctly! Yea!

[crquisto]

You'll still need to address the odor overboard problem now that you have no vent filters. NoFlex Digester will do it.