I could not find a stock tank that would meet my criteria. I wanted it to take up no useful space, sit as low as possible in the boat, and as close to the toilet as possible. I think this fills the bill. The only negative was price. Custom aint cheap!

First view of tank

This should give you an idea of the wedge shaped character of the space.

Other end of tank.

I cut new plywood to replace what had been cut out of the floor. Used aluminum stock to make a mounting flange. Painted with a bit of anti-skid. Visable are input, dip tube for pump-out, vent, and an inspection port with a clear cover. Ever so much more accurate than some gauge. If extreme accuracy is needed I can screw off the cover and check with a dip stick if I really want to.

The tank holds about 20 gallons, sits low in the boat in useless real estate, and is only a 1 1/2 foot pipe from the toilet. Sure beats a stinky bag.

How it looks finished, more or less.

The tank is below the floor of the starboard cockpit locker where the engine cooling through hull and pressure water pump were located. Those were moved to other, better locations and the remaining hole through the skin was filled with glass cloth and epoxy.

The triangular piece in the upper left of the picture was a small floor where the water pump was mounted. It came out with much hacking with a sawzall and circular saw on a 10 degree Sunday. It dawned on me this might not have been the best idea with the boat still in the water.

The hole the tank went into