Did the final fit and installation of the grey water tank this past weekend. Unlike the fuel and water tanks, this one can never be removed. The length of the tank is 47 1/2″ inches which is exactly the length of the aft center compartment including the 1 1/2″ thickness of the bulkhead. Capacity is 18 gallons. The installation was done by cutting an opening in the lower bulkhead between the engine room and the main salon, under the center fuel tank compartment. Then the tank was slid through the opening, into the compartment from the engine room. Cleats to secure one end were fitted on the opposite wall, and two cross members fitted with cleats on the underside, are used to hold the tank down, and keep it from shifting from side to side. The cross members also help support the fuel tank above.
The tank is not lying directly on the bottom of the bilge, but, two feet made of fiberglass u-channel are tightly strapped to the underside to keep the tank up off the bottom. Strapped because nothing seems to adhere well to polyethylene. Truth be told, it can still be removed for now, but once the engine room gets filled out (like with an engine) there will be no space to slide the tank out completely.
Any future maintenance on the tank (like cleaning) will have to be done via the 6 inch inspection port mounted on the top near the aft edge. As long as 9 inches is kept clear aft of the tank, the hold down bracket can be unbolted and the tank slid out to reveal the inspection port. Should something foul the tank beyond use in the future, that cant be fixed via the inspection port, it will need to be abandoned in place, until fuel tanks and/or engine come out (hopefully never).