Scale back on outlet pipes

We bought our previous boat, (a Sadler 34), in 1995, and although she was over 10 years old she was in very good condition.

The only problem we encountered in the first 12 months of ownership was the loo being blocked by heavy fur scale inside the outlet pipe: the bore had been reduced from 50mm to 10mm! We discovered that this is a common problem with sea toilets, so I carried out some research to ascertain the cause and prevention. The solution turned out to be remarkably simple, and these blockages are absolutely avoidable without any plumbing modifications or costs.

I had read that there are calcium salts dissolved in seawater. When mixed with urine they precipitate a scale coating inside the loo, its rubber valves and the inside of the outlet pipe. This is very similar to the fur scale found inside kettles in hard water areas (although the cause may not be the same!). These scale deposits build up until they jam open the joker valve and/or block the outlet pipe. This can happen within only a few years, so what’s the simple solution?

Pumping regime

All you have to do is pump all your waste out of the system every time you use it. A good 10 pumps of clean seawater after the last of your waste has disappeared should be enough. Remember to tell all your visitors to do the same.

We have adopted this pumping regime since 1996 and have not had any scale build-up in our loos or pipes. I had cause to check the original loo outlet valve in our current Dufour 40, which we have owned since 2004, and there were no white scale deposits anywhere to be seen after 12 years of regular use.

Once you have scale which is restricting flow inside your system, the ‘10 pumps’ regime will not clear it out. There are proprietary chemicals that claim to clear scale, but heavy scaling may need more drastic action. If you think you could have scale in your outlet pipe, here’s one way that might shift it. Get a pair of grips big enough to grab the outlet pipe. Gently squeeze the outlet pipe nearest to the seacock with the grips to deflect its sides by no more than 5mm and give the loo a few pumps on ‘wet bowl’ to flush it away.

If you have no scale build-up you will not feel any scale breaking free, and if you cannot deflect the pipe sides it may be that the scale is too thick. If you can feel the scale cracking free, continue this process, working your way back up the outlet pipe until it has all been cleared.

Be aware that this process could dislodge enough scale to block the pipe, but if it’s that bad you’re probably ready for a new outlet pipe anyway. Better to find out now than when you have guests on board!