We have two 35 gallon tanks on out houseboat. They are used in tandem. The drains are connected to each other and to a T-junction. The hose from the T-junction goes up to the deck plate. The vents are also connected in tandem.

The head is an electric macerator type.

The head empties into the top of one of the tanks and the effluent flows between the tanks between the drains.

I am trying to check for certain today, but I think one of the tanks may not be getting pumped out. Maybe some sludge is in the drain area of fitting.

I have not been using any treatment for the tanks to reduce sludge, though just got some.

If one of the tanks is not emptying, do you have any thoughts?

Could I use muriatic acid? Would a few gallons eat through the sludge and loosen it up?

I would like to avoid opening the tank if possible.

What material (drain cleaner, etc.) breaks up tank sludge?

Should I try blocking the vent to the tank that is OK, and force water down the outlet? This might make the flush water push into the full tank. Maybe not a good idea if it is really full!