Based at Southwold on the East Coast, we generally have two choices when we leave the harbour. Turn right, or head straight across the North Sea. Us locals try to avoid turning left! Heading straight across means that in 12 to 14 hours we’ll be in Dutch or Belgian waters, and among the myriad of required items we should have on board or fitted is a waste holding tank – especially if we want to visit the inland waterways.

The trouble is, many of the boats produced in the 1980s and ’90s really didn’t take this into account, so it can be quite difficult to work out where to put an additional tank of 100+ litres. Most of the obvious places to fit a tank already have one, so it means we have to get a bit creative.

Lucky for us, Tek-Tanks allows us to do just that, and will build a tank to fit some really weird spaces. I’m sure there are other tank builders that can do this as well, but we tend to stick with what we know works for us.

Designing the waste holding tank

Anyway, it so happened that an Oyster 406 came in for a new Beta engine, a new electric loo and a waste holding tank. While our engineering boys set about tackling the ‘how do we get the old engine out?’ issue, I got on with measuring the total cupboard space above and behind the forward heads. And as long as the owners could find a new location for their toothbrushes and shampoo, I believed I could get a 110lt tank in there.

The old cupboard is stripped out to let us take a better look at what lies behind it. Credit: Mike Pickles

Yes, it was a strange shape – a bit like a giant wedge of cheese – but nothing out of the ordinary for Tek-Tanks, who have come up trumps every time I’ve set them a challenge. It would require a little bit of surgery to the boat interior and also some thought to ensure there would be adequate access in the future.

Original builders/designers tend not to lose too much sleep over enabling access to things that could require maintenance work later on, with quite large areas of boat that are virtually impossible to get at.

Removing some bulkhead reveals a much bigger space. Credit: Mike Pickles

Being sailors and boat owners ourselves (coupled with the frustration of getting to fittings, bolts, pipes and cables, plus hull areas you need access to in case some numpty T-bones you in a marina), we like to make certain that whatever we put in can also be removed; and we also attempt to provide access to hitherto no-go areas.

We could have totally filled the available space and found another 30lt of tank space, but access would have been made much harder to the top fittings such as the air filter/breather, flush-out and level sender, so practicality won the day. The heads moulding is quite tight to the hull, so the skin fittings are forward of the main bulkhead in the forward cabin.

Changing fittings

Changing fittings, including toilets, will always result in redundant and unsightly holes, so this dictated the location of the access hatch – and that in turn finalised the position of the diverter valve. The electric loo switches were mounted through 5mm white plastic sheet glued to the side of the sink cabinet, again covering a number of redundant holes.

Creating a hole for the connectors and pipework. Credit: Mike Pickles

We could have glassed and re-gelcoated, but the extra expense was viewed as being unnecessary. The one issue I have with electric loos is that they are so incredibly noisy, despite being named ‘quiet flush’. There should be a little flag raised whenever you use one in a marina, saying: ‘Yes, we have a holding tank’.

A hole covered by a hatch allows access to connectors and pipework below tank. Credit: Mike Pickles

That said, the Jabsco works well, and based on the lack of complaints from customers they seem very reliable. This is the first time I’ve used the Jabsco diverter valve, and I’m hoping it proves reliable as fitting it was a breeze, especially as the outlets are movable and allow many angles for the 38mm pipework.

More than adequate

During testing the loo and inlet pumps proved more than adequate to discharge into the waste holding tank, and with the diverter valve set to ‘empty’ the tank level dropped like a stone. An initial worry was about having 100kg of extra weight up high and out on one side, but once the boat was on the water it made very little difference visually – and, of course, once offshore the tank could be emptied anyway.

The ‘silent flush’ loo gets a trial fit. Credit: Mike Pickles

The owner’s report back was very positive, and apparently the noisy loo issue is not as bad as I feared as it takes such a short time to flush and pump.

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