SAIL - April 2015

BOAT

WORKS

BOAT

WORKS HOLDING TANK 101

to take the discharge hose from the tank.

Depending on how your boat is laid out,

you’ll have to make some kind of a sacrifice

when you install a gravity drain tank. In my

case, I had to surrender most of the boat’s only

hanging locker. I located the tank as high as

possible under the side deck, partly to retain

useable space underneath it, partly to help

gravity do its work. It stands to reason that

the bigger your boat, the easier you’ll find it to

install such a tank. The good news is that since

you will most likely have to have the tank made

to measure, you can make use of odd-shaped

spaces that are no good for anything else.

THE UPSIDE

In a word, or rather, two words: user-friendli-

ness. It is hard to make anything foolproof on

a boat, given that fools can be very ingenious,

but this is as close as it gets. There are, however,

a couple of quirks to the system. Depending

on the type of toilet you have, you may have

to pump more water through it to ensure all

the waste is moved past the bend where the

discharge hose enters the tank; you don’t want

waste water draining back into the bowl.

If there are any right-angle bends in the

discharge hose—for instance if it tees into

the standpipe for the deck discharge, as mine

does—it is also possible for blockages to form.

You can get past this by sailing with the dis-

charge seacock open, so seawater flushes any

residue out of the tank and pipes. If you want

to be sure you’ll never have a blockage, practice

the nothing-you-haven’t-eaten rule and don’t

put paper in your toilet. When we leave the

boat, we pump a bowlful of clean water through

the plumbing to clean out the discharge hose.

Every couple of weekends, we also pump a gal-

lon of white vinegar through the system and let

it stand with the seacock closed. This cleans the

scale off the insides of the hose. We have never

had a blockage or any other issues.

In the years since I removed our boat’s

ancient holding tank and its snake’s wedding

of seeping plumbing from its malodorous lair

beneath the V-berth and replaced it with a

gravity tank, I have seen the world’s produc-

tion boatbuilders go the same way. Why? Two

reasons—with its minimum of moving parts,

such a system is easy and inexpensive to install,

and it is simple to use. s

The discharge hose from

the tank is teed into a

hose running from a

pumpout fitting on the

deck to the seacock

Repair your hatches without

costly replacement.

Select Plastics, LLC is Lewmar’s

approved master hatch repair facility

for North America. Select stocks a

full line of repair parts for all makes

and models of deck hatches.

THE GREEN

ALTERNATIVE

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