Monday, April 4, 2011

Implosion prevention

What happens if your holding tank vent gets clogged?  It could be a bug building a nest in the vent fitting out on the stern.  Or it could be "stuff" pushed up into the vent by overfilling the tank (oh, there's enough room for one more flush, isn't there?).  Whatever the cause, having the vent line blocked is a problem.  If it is almost blocked, then you will probably be unaware of it during normal head usage, because the rate of inflow is small.  Ah, but during pump out, when the flow rate is much, much higher, problems can occur.  How to protect your boat from this event?  Paul on s/v Solace has this helpful tip for us:
While pumping out my holding tank, I heard a crackling sound of fiberglass. Stopping the pump out, I noticed the holding tank was starting to implode and the fault was a blocked vent line. To prevent a disaster happening in the future, I installed two Tanksavers from Sealand. These offer a one way valve which will open if it detects too much vacuum inside the tank. With those big dockside suction units, this could be the one thing that could save your tanks.

A three inch hole saw and a Tanksaver kit from sealand costing about $20 is required.

 Find a flat surface on your holding tank top surface and drill the 3 inch hole. Push in the rubber ring and then coat the valve insert with dish washing liquid and push in. That's all there is to it. Just a ten minute job on each tank.
Hole drilled and rubber insert placed

Finished product


  1. Question whats to prevent odor or heaven forbid waste to seep out? Our holding tank is under the v-berth.


  2. John,
    No odors experienced. The rubber bung/grommet fits tight into the cut hole and the sprung valve fits tightly into the bung/grommet. The valve is sprung loaded with a rubber seal. It was hard for my fingers to push the valve open. The only way I see it opening is if there is a decent vacuum created inside the tank. With the rubber seal, I don't see any possibility of waste leaking; even if under pressure. Important to cut the hole with a hole saw, not a jigsaw or other device. A perfectly round hole will ensure the bung seals well around the hole created.
    Hope that helps. Paul sv Solace


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