Systems+Engines

Gravity Theory

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Smell. Pong. Effluvium. Whichever way you describe it, the airborne essence emanating from Ostara’s aged sanitation system was highly unpleasant. More than just an odor but thankfully short of a full-blown stench, it permeated the forepeak and almost caused a spousal mutiny during our first weekend aboard. No doubt about it – something had to be done.

The sanitation system comprised a Wilcox-Crittenden toilet connected to a Vetus bladder-style holding tank under the V-berth. The toilet pumped out via a 3-way diverter valve, which directed waste either into the holding tank or out to sea. A dedicated pump to empty the holding tank was connected to the diverter valve via a T-piece. The diverter valve and the pump were under the bunk in the forecabin along with the flexible bladder holding tank.

The holding tank did not have a vent. It had a long outlet hose going through the bulkhead into the anchor locker and up to a waste pump-out fitting on the foredeck. The outlet hose leading to the outlet seacock had a vented loop well above the waterline. There was no anti-siphon provision in the inlet hose; its entire run was below the waterline, risking water flooding the boat via the toilet bowl if the lever was left in the wrong position and the inlet seacock was open.

All in all, this was a most unsatisfactory system. Not only was it needlessly complicated and awkward to use, there were too many connections with the potential to leak and cause odor, and waste tended to sit in the long runs of pipe (as I discovered when I was removing the old hoses from the boat). The bladder tank under the V-berth was poorly secured, unvented, and smelly. With no breather, it would have been all too easy to overfill the tank to bursting point. Enough said.

So, after consultation with a couple of friends who’d done the same thing, I decided to replace the holding tank with a gravity drain system. This is simplicity itself. All you have to do is mount the holding tank so that its bottom is above the waterline when the boat is at rest, and its top is above the waterline at the maximum angle of heel. The toilet pumps directly into the tank, and the tank drain directly to the outlet seacock. To empty the tank, you just open the seacock, and gravity takes care of the rest. As an added benefit, the motion of the boat through the water will force seawater up through the outlet hose and into the tank, thereby rinsing it out. With the seacock closed, you’ve got a legal Type III MSD if you have also plumbed a deck pump-out fitting into the outlet hose.

There is no need for a vented loop on the outlet hose, because the vented tank acts as a siphon break. The inlet hose should be looped above the waterline and, depending on the toilet you use, fitted with a vented loop. A breather hose also must be plumbed into the top of the tank.

I’ve had to unclog blocked heads a couple of times too many; going over the side with a wire coat hanger to ream out the outlet pipe or stripping the pump to remove a wad of toilet paper gets old pretty quickly. That’s why I decided to junk the veteran Wilcox-Crittenden with its faithless joker valve and treat the boat to a Lavac. This British-made toilet has no moving parts. It operates on a vacuum principle that, not to put too fine a point on it, macerates the contents of the bowl to the point where there’s nothing big enough to get stuck anywhere. I’ve never heard of one clogging up, plus the Lavac is extremely frugal with flushing water – a mere 3 pints per flush – which make your holding tank go further. This is vital when you’re cruising with the family. It’s pricier than the Par/Jabsco budget toilet but cheaper than the upscale thrones from Raritan and Groco. Anyway, what price peace of mind?

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