Holding tank build-out

[captainVT]

Need to increase the size of the current holding tank for the head from 5 gallons to much larger tank size. Current site of 5 gallon holding tank does not allow for larger tank. Currently, holding tank is near the head on port side under settee. Starboard settee has ample space for a 30 - 40 gallon tank, depending on shape, but there is limited space for running the plumbing.

Rather than relocating all the lines / plumbing to the starboard settee (which will be difficult to impossible due to space limitations), could I just add a 2nd tank with an overflow line such that I only had to relocate / add 1 line? Would this cause issues with pump-out? Or other issues?

Boat is currently lake sailed, discharge overboard has been disconnected.

[CaptainForce]

I would think this would work best with the connection between the two tank at the lower portion of the tank and the pump out on a "T" between the tanks with both tanks vented. 'take care and joy, Aythya crew

[captainVT]

Venting was a concern, but could easily locate pumpout T near current 5 gallon tank and should have room to vent 2nd tank.

Any issue you think with venting both tanks on 1 line? Wouldn't think so as household plumbing is done in similar fashion.

[billyruffn]

Venting is definitely a concern, but also think about how you'll suck the s**t, (er, biological liquids) out of the second tank.

[scottyt]

you would not want the pump out line to be a T between the tanks. it could only empty one side, if the other has the slightest blockage.

honestly if you can run a line between the 2 to have it use both tanks, you could just run a new line from the head to the new tank, the longer line wont really matter, same with the vent and pumpout point. remove the old tank and run new longer lines.

i really think you are asking for problems if you try 2 tanks. its just 2 2 inch lines to extend, if you tried an interconnect line it would need to be at least 3 inch just to get "stuff" to flow between the tanks

[sailingdog]

Multiple holding tanks for a single head is a bad idea IMHO. You're much better off with a single tank and running the hose properly. Venting and pumping out are both concerns.

[jbondy]

Re venting, I'd read a recommendation intended to keep odors to a minimum that there should be two vents on the tank, one to each side of the boat. The vent from the port side of the tank would go to the starboard side of the hull and vice versa. The same recommendatio said that most vent hoses are undersized. A 1" hose and vent were recommended. The idea is to allow a flow of air.