Installing a Marine Holding Tank

Before too long, if you haven't already got a marine holding tank in your boat, you're likely to find - particularly if you sail in the more heavily trafficed parts of the developed countries of the world - that substantial areas of your favourite inshore cruising grounds will be out of bounds.

It's true that for years, we sailors (along with fish, birds and other mammals) have been polluting the oceans - and nature has easily been able to deal with it.

But in recent times, recreational sailing has mushroomed, and where we have flocked together in anchorages and ever-larger marinas close to towns and tourist areas, our concentrated efforts are often clearly visible.

Clearly, this isn't good news for the environment; something has to change...



International Legislation

Although there's currently no consistency at European level on the matter of holding tanks for recreational craft, some EU member states have enacted national legislation limiting access to certain areas to those vessels equipped with a holding tank, whilst others are still sitting on the fence.

Sooner rather than later, yet more EU legislation will befall us here in the UK, and we'll all be required to install a holding tank - or in the language of officialdom, a Marine Sanitation Device (MSD).


Beware the 'Potty Police'!

In the USA the requirement is already pretty much universal, and enthusiastically enforced by the waterborne 'potty police'. These gentlemen will board your boat uninvited, and if they find your holding tank diverter valve in the 'discharge' position, you'll find yourself in a spot of bother.


Holding Tank Installation

installation of marine holding tank systemA typical holding tank installation

Artwork by Andrew Simpson

This arrangement, through appropriate use of the diverter valve, will either discharge toilet waste overboard or to the holding tank for proper disposal later.

Retro-fitting a rigid plastic marine holding tank is likely to test the ingenuity of most boat owners, who will already have claimed all suitable spaces for other useful purposes.

A flexible holding tank may provide a solution, although if it chafes through it will provide rather more. Whatever type of tank you decide to use, remember to use sanitation grade hose for all pipework other than the inlet, and double-clip all hose connections.


Ensure there's Adequate Ventilation!

To avoid unpleasant odours and disperse any gaseous arisings, the vent pipe diameter should be not less than one and a half inches (38mm) and exit the hull side just below the gunwale.

Wherever possible it should be left permanently open to allow both the discharge of displaced air and the free flow of incoming air, thus retaining the effluent in an aerobic state.

If the breather pipe is smaller than this, ventilation will be inadequate and the contents are very likely to turn anaerobic - and decidedly smelly!


A Simple Alternative to a Plumbed-In Marine Holding Tank

For a small boat with no plumbed-in toilet, a Thetford Porta Potti may represent the ideal solution.

These require no plumbing and have a reservoir of fresh water for flushing bowl contents (or should that be bowel contents - sorry, couldn't resist it) into a removable tank which is carried off the boat and, er, dumped. 

They meet all the requirements of a marine holding tank, so should you get a visit from the potty police you'll be in the clear.

It's a very good idea to make sure you've properly installed the hold-down kit...



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