We planned to tackle the holding tank this weekend.  Our goals were pretty simple: install new discharge pipe, pour some holding tank treatment chemical and water into the tank, let it sit for a few days, pump out the tank.  What did we accomplish?  Not a lot.

We put water into the tank through the inlet side with a scrap piece of pipe.  As we were doing this it sounded like the tank was filling up.  Actually, it sounded like as if a pipe was filling up.  So Rich stuck an old wire coat hanger down the inlet side and it looks like there’s a dip tube that goes all the way to the bottom of the tank.  So with the scrap piece of pipe we tried to put some water in through the discharge side and water came up the inlet side and just sat there.  Rich went up to the cockpit to get something and the boat rocked a little and the water blub, blub, blubbed back down into the tank.  Rich put the coat hanger down the discharge side and we can’t tell if there’s a dip tube.  We’re pretty confident that we’re not confusing the inlet and discharge fittings because they face opposite directions (the inlet fitting faces forward toward the toilet and the discharge faces aft toward the deck pump-out), but it looks like someone at some point did confuse them and they’re not installed correctly.  So back to the drawing board; we figure we have a couple of options:  1) install the new pipe on the fittings we have, but switch the inlet and discharge and hope they work; 2) install a new discharge at the bottom of the tank to eliminate the dip tube and use the existing discharge fitting as the inlet; 3) cut off the inlet and discharge fittings and reinstall them correctly.

The problem with option 1 is the direction the fittings are facing (forward and aft).  We’d have some crazy sharp turns in the pipe if we switched the inlet and discharge.  Option 2 is a crap shoot because we’re not sure where the bottom of the holding tank is.  If we drill too high, we’ll never be able to empty the tank and too low means a hole in the keel.  Plus, with option 2 there will always be black water sitting in the discharge tube when there’s any liquid in the holding tank so eventually that pipe is going to start stinking.  Option 3 is probably our best bet.  We already have to cut off the vent line fitting because it’s totally clogged so cutting off all three fittings might be the only solution.  We’re going to remove the water tank in a few days so there should be enough room to accomplish this.  We might rent one of those sewer cameras to TV the inlet and discharge to see if one or both have dip tubes.  If only the inlet has a dip tube it will become the new discharge side.  If they both do, then we’ll have to cut one off for the inlet side.  Oy vey!  Gotta love boats!  Oh, yeah…and Rich lost our main halyard at the top of the mast, so now I have to haul his butt up there to retrieve it before we can remove the water tank.

On a happier note, Rich painted two coats of Awlgrip in the refrigerator.  It looks fantastic!  We’re really close to having cold Gatorade without the use of ice packs.


Car Ride - Round Two
What a day!


  1. Rich-
    I think that the pipes are correct.

    The forward most hose was originally dual purpose. It was the toilet to holding tank line, fed by gravity. It also served as the overboard black water pumpout.

    It achieved this with a hand-activated diaphragm pump under the sole, just aft of the mast and a manifold of gate valves in that same vicinity.
    The pumps output is just above the waterline inside the SB single hanging locker.

    WARNING: most T37s do not have a vented loop at this thruhull, making it prudent to keep this sea cock closed unless in use OR installing a proper vented loop inside the locker.

    This pump also serves as a bilge pump, again by using the gate valves. On my T37 the bilge pump hose was run SB under settee back to valves and pump.

    The other fitting at the aft end of the holding tank is for the on deck vacuum pump out. Because a heavy vacuum is drawn and the valve on the line from the head is closed when they pump out, the tank is evacuated of air and waste.

    Of course, T37s are all a little different, so what I have may differ or been changed on your vessel.

    As others have said the basic system is a real rats nest, with long smelly runs and lots of hardware.

    I decided to bypass this whole mess and installed a composting toilet. No regrets. KISS

    If you have any questions or I’ve not been clear, just drop me a line

    Fair Winds,
    Ed Halbe

    1. Thanks Ed, it sounds like we have pretty much the same plumbing layout. Plan is to abandon the waste pump-out loop through the floor mounted bilge pump (saving it for emergency bilge water only) and go with a Mark 5 pump in the engine room for overboard discharge. Same pump out new Lavac head uses, so spare parts are universal. Holding tank vent was plugged, so I think that may be the reason the tank never fully emptied, but I’m still looking into that one….

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