Water-balancing Manifold


Balancing Act

Water-balancing manifold

Water-balancing manifold

Keeping the boat in “balance,” that is, keeping it from listing to one side or the other, is an ongoing project. It is generally done by moving fuel from one side to the other with some type of fuel filter/pump system. That works well unless both tanks are full, at which point the only real option is to balance with water. Unfortunately, the standard plumbing on a 1985 DeFever 44 (ours at least) does not accommodate transferring water from one tank to the other. And to make it worse, since the two tanks are connected by a “T” fitting just before the pump, water can gravitate from one tank to the other, so once it is out of balance gravitation could, and at times does, make it worse.

It was this frustration I was addressing as I set out to build a water-balancing manifold which I could use to both transfer water and easily select from which tank water was drawn to supply the pump. After playing with several options and with the help of a friend in the residential water business, we came up with manifold with 4 valves that allow selection of tanks and movement of water between tanks using the existing pump.

water-balancing-manifoldThe input lines from the tanks feed each side of the manifold, which is placed before the pump. There is a “T” placed in the output side of the pump which leads back to the manifold. The top valves determine which tank is feeding the pump, and the lower valves, if opened, determine which tank receives water. With the top port side tank valve (1) open, top starboard side tank valve (2) closed, and both lower valves closed (3 & 4), the pump is fed from the port tank and no water is transferred (as diagramed in figure 1). If the lower starboard valve (4) is then opened, water is pumped from the port tank to the starboard tank. This requires that the original valves located at the bottom of each tank (5 & 6) be in the open position, which reduces the amount of gymnastics required to open and close tank valves – especially in the middle of a shower or in a hot engine room. If you want gravity to move the water, simply open both top valves (1 & 2).

The entire manifold was made with John Guest press-on plastic valves and fittings and 1/4” plastic tubing mounted on a 1/2”piece of plywood with nylon ties (all available at Home Depot for about $50). Once assembled, the manifold is mounted in a convenient location where the input lines from the tanks can be routed to the manifold. (I mounted it to the aft bulkhead in the engine room just above the pump.)

All the parts easily slipped together and installation was simple. Simply cut the “T” out of the original copper supply line, clean the copper with emery cloth, and slip a press-on 1/2″ to 1/4″ fitting on the ends. Run a 1/4″ line from each tank to the manifold. Out of the top of the manifold, run a 1/2″ line to the input side of the pump. Place a “T” in the output side of pump line which runs to the bottom of the manifold. Close the valves on the manifold, open the valves at the tanks, and turn on the pump. Checks for leaks. Then next time your boat is out of balance, just open/close 2 valves. (I suggest you set a timer. I can normally get from a fully pegged bubble on my level to level in 10 to 15 minutes.)

I initially thought of building this unit with copper, but when I went and priced copper, determined that if these plastic fittings were good enough for higher pressure of new home construction, they would work for this application. Plus the worse case scenario would be to have both tanks drain into the bilge through 1/4” tubes, well within the capability of a normal bilge pump.

Though I was concerned the 1/4″ lines would not supply enough water to the galley sink and showers, they do just fine. (The entire manifold could be made with 1/2” lines if preferred.)

If you have any questions, please feel free to contact me through the comment box below.

Water Manifold

Water Manifold


Copper "T" replacement

Copper “T” replacement



  1. It’s good to see someone thinikng it through.

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