Boat Plumbing – Part 2 – The Plot Thickens

September 16, 2018 Peter No comments exist

The initial plan was to replace all the pipes in the head on the assumption that they were the offending items and doing so would solve the problem of the nasty smell on the boat. We purchased good quality sanitation grade piping and replaced all of the outlet pipes from both the head and the black holding tank. This is not the most pleasant of tasks but after about a week we had managed to replace these pipes. We also ordered a new flapper valve even though we had replaced it in Adelaide less than a year ago. The flapper valve (on some systems referred to as the joker valve) is designed to stop water flowing back into the head and we had water flowing back into the head once we flushed the head.


Whilst doing the research for this project we read as much as possible to try and understand the plumbing and how it all functioned. We came across this article by Don Casey on how to install a head which proved very helpful. We have Don Casey’s Complete Illustrated Sailboat Maintenance Manual which we find a really good resource. It now appeared that we had a new problem. The vented loop on the inlet side which prevents water siphoning back into the boat was fitted between the seacock and the pump whereas it should have been fitted between the pump and the head. The vented loop was in fact causing the pump to draw in air and water when the pump was activated. We would now have to redesign the inlet piping for the head.


It was also time to test the pump for the black (or waste) holding tank. The system is designed in such a way that by changing the position of the Y-valve the waste is pumped out of the black tank and discharged overboard. A separate Y-valve controls where the waste from the head is sent – either directly overboard or to the black tank. We disconnected the outlet pipe for the black tank from the Y-valve and put this into a bucket and activated the pump. The waste should have been drawn out of the black tank and deposited into the bucket. That, at least, was the theory. We could hear the pump running but nothing came out of the pipe. Further investigation revealed the problem. The pipe from the black tank to the pump did not actually go into the black tank but was simply connected over a filler type pipe mounted on the black tank. There is no way in the world it was ever going to work and it had clearly been installed just to satisfy the authorities if they ever did an inspection. Trying to drain the black tank with this arrangement would be like trying to drain a bathtub with a vacuum cleaner, it just isn’t possible. To complicate matters, the black tank was three quarters full and clearly had never been drained. What were they thinking!

To add to the problem, when we lifted the floor in the passage next to the head there was fungal growth. It was clear that water was leaking into this area. There were only two possibilities, either the inlet seacock was leaking or the black tank was leaking. We eliminated the inlet seacock as an option which left only the black tank. It would be possible to remove and replace the black tank but this would necessitate removing the head floor. Given the magnitude of the problems it was time to look at some alternatives.

We had some time ago come across composting toilets and thought that if we ever had to replace a toilet in a RV or a boat we would seriously consider a composting toilet. Those that have them rave about them. They have their challenges, but then so do all toilets in RV’s and boats. It was time to have another look at composting toilets.


But first we would have to find some way to drain and flush the holding tank. There is little doubt that the holding tank and the leak from it are the cause of the nasty smell on the boat. At least we know what the problem is, now we can fix it.

The Kangaroo in the picture at the top stopped by to say hello as I was walking from the boat to the caravan one evening.

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