Holding tank treatment

[madhatter1]

Found the culprit. Well, Capt Dave explained it to me. One previous owner had the holding tank converted for extra fuel capacity. After that owner it was changed back. But when changed to fuel a high vent was installed next to water vent. Smaller vent line was installed. This explains exactly what was happening. Flow would slow down due to small vent line and resume once vacuum was broken. So just a project to go back to correct size vent in original location this winter.

[jmooney]

I have used a product called Noflex Digestor. Seems to work well. I would like to hear comments from any other users.
l had a similar problem with pump outs. The cause was corroded stand pipes . I have two pump out systems , one is the factory pipe and the other is an on board Oberdoffer pump.
My holding tank was also used as a fuel tank, so I had to change the high fuel vent back to the lower original location. Since the original vent fitting was one inch, I used one inch vent hose.
I replaced the large stand pipe with cupronickel, pvc might be better. I left approximately one inch clearance between the pipe and the tank bottom. The smaller pipe I replaced with pvc.
So far no problems , but I have noticed most pump out systems are very weak. This might be a good thing , as fiberglass tanks can’t take over pressure/vacuum.