Adding a Spare Holding Tank (U-shaped Dinette)

by Bill Matley

The spare waste tank setup I employed is based upon the premise that..."on rare occasions, I may need additional waste storage for a few extra days, before I can get to a pump out station." My spare waste tank has only been used 3 times since installing it in May 2006, but each time I needed it it worked great and saved the day!

The installation is straight forward and easy to understand. The spaces are small and the waste hose is difficult to manipulate, making the job more difficult that it should be. The hand drill hole saw does a great job but makes a big mess, and this adds to the difficulty. All things considered, I am glad I made this upgrade; and it works just great.

The first photograph shows the two storage spaces I used for the spare waste tank project.

U-shaped Dinette Forward Settee Compartment

The second photographs shows the cardboard template I used to locate the holes for the Todd 6 gallon plastic tank and the 3 tank hoses (input, pump-out and vent).

Cardboard Template for Holes

The third photograph shows how I installed a "Y" valve in the (toilet to primary waste tank) hose. I then attached a second waste hose for the input (top barb) of the spare waste tank. You can also see the tank and it's 3 hose barbs, as well as the nylon strap I used to hold the tank in place. As I said, it’s not very complicated. Buy a good "Y" valve - this isn't the place to save a couple bucks. Mine doesn't leak and I like it that way!

New Y-Valve to Select Spare Tank

The fourth photograph shows the cabinet behind the toilet with the doors taken off. How did I get the new hose holes to line to up? I started by drilling the deck hole first, and then dropped a plumb bob down the deck hole, marking the centers and drilling as I went.

Head Cabinet Showing Hoses

The existing vent runs up to attach to the base of the stanchion.

Did you all know that the toilet waste system vents out of the port stanchion? You should take note of this plumbing design detail. There has been plenty of talk about boat toilet smells on forums all over the Internet. If you or a previous owner ever overflows the waste tank, paper and other foul stuff is going right up this stanchion, and will stay in this stanchion. This will stink and will cause your toilet system to be starved for air. So if you have overflowed your waste tank, start cleaning here. If you have never overflowed your waste tank and your system works well now, don't overflow it in the future.

The next photo shows the new waste tank pump-out hose that I installed.

New Plumbing

The vent hose from the spare waste tank "Tee's" into the existing vent. It also shows the spare tank pump-out hose routing out to the cabinet behind the toilet and eventually to the new deck pump-out.

The sixth photo shows the location of our existing primary waste tank pump-out and the new spare tank pump-out fitting, about 8 feet further forward.

Deck Pump-out Fittings