Holding Tank

Although not a requirement in the UK i think it probably should be, it is a requirement in other countries though and also officially needed for the canals although by all accounts not really checked. I looked at where to put it and there wasn’t much choice. My Dad thought I could make a box and put this under the toilet itself, this would have maybe been easier to install but I was worried about the toilet height as HWMBO already found it high. There was space fore of the heads under the V berth but the plumbing would be a hassle and the advice of other yachties when putting a tank in was to keep the pipe runs as short as possible. After having a good look behind the toilet I thought there was enough room to get a small tank in.


The main problem was, as usual, there wasn’t a straight buy-and-fit option as the space I was thinking of putting the tank was small and needed a specific size and shape. The only way I could do that would be to make my own tank which would mean a healthy amount of fibre glassing. There were several pages on line that helped but this was the best and most like the work I would be doing: Greyhawk Refit There were some great pictures on there for me to try and replicate as well as a great description of the work, so thank you Mr Allen.

I started off making a back to the tank, I did that by taping a plastic sheet to the area I want the tank to rest against and then fibre glassed over the top of it. This worked to some extent but unfortunately the plastic slipped slightly so I was left with a rippled fibre glass sheet. The items that would be going into it wouldn’t care about the aesthetics but it was slightly annoying. Next i made some sheets of fibre glass by using a metal sheet and just fibre glassing straight onto this, when dry it was easy to flex the metal sheet and I was left with a nice sheet of fibre glass.

I did this four times to varying sizes for the sides and top. Once I had enough sides I taped the sheets together roughly, if there was too much overlap I just cut the excess off and was left with a box shape, I then fibre glassed the sides together.

This worked reasonably well but I could not get the box watertight (fairly important) no matter how much I fibre glassed and I was also running out of time as the leave date for France was drawing closer. In the end I found some POR15 Flexible Fuel Tank Sealer Repair on ebay which seemed to finally get all of the leaks plugged after two coats.


Before using the sealant I did add the lid, which needed several inlets and outlets and I also added an “observation window”:


A lot of making the tank was getting the right sizes of things, the existing hosing was a standard marine sanitation hose of 38mm which apparently is unique to boats. As the above shows there’s also a breather on the top right, input is top left and output for pump out bottom left. I also drilled an out to be able to empty the tank, this led to a manual bilge pump.


I then drilled a hole through the deck in order to be able to connect the pump out. This went ok although had to involve a bit of guess work at the end to try and get the outlet lined up.



From left to right, drilled hole through deck, drilled hole through shelf behind heads and deck fitting for pump out.

Finally there was the job of putting the tank into the tiny space and getting all the pipes connected, to my amazement it actually fitted and with some persuasion and a lot of swearing I finally had the tank fitted. My final job was to box everything in to make it look a bit better. We lost the cupboard space behind the toilet, although we never used this, but gained a small shelf above the holding tank which was really useful. The manual bilge pump works with water at least, fingers crossed it works with something a little more substantial.