Ken Surplice
My 275 has a holding tank just forward of the sail bath in the forepeak. I pump it out using a Whale manual pump mounted in the wet locker area.

I’ve often wondered if I could simplify the system and use a gravity drain for the holding tank. Before I start working out where the waterline is May I ask if anyone tried it?

I’m aware of at least one boat that has a small thin holding tank fitted high up behind the bulkhead in the heads, behind the sink bowl. I’m investigating the feasibility of gravity draining the tank forward of the sail bath
Martin Watson
How is that going to work Ken when the tank is below the water level? The tanks that are high up will naturally drain because they are above the water level but if you had a through hull below the tank, the tank would fill up with sea water when you opened the valve unless you had a loop in the pipe that extended above the water level and then you would be back with the same issue I assume you have now, in that you need to pump it out. Have you considered going down the composting head route? I fitted one this winter before I set out on my circumnavigation and it has been a resounding success, with no significant smell issues and the bonus that you don't need any through hulls. It is also very green because you just end up with compost which can be put in a normal waste bin Inside biodegradable bags) and urine which can be carried off and poured down a normal toilet or poured around the base of a mature tree if in the country. I have had the through hull fittings glassed over before I had the boat re copper-coated and I'm sure it has even made the boat bit quicker too! I'm also not polluting the harbours and marinas I have visited either. I will definitely add one to any future boats I may get.
Martin Watson
Ken Surplice
Hi Martin, many thanks for sharing your advice. At present my setup is that all effluent goes into the holding tank. A manual whale pump is dedicated to emptying the tank. I asked the question in case there was a possibility to simplify the plumbing. I’ve not measured where the water line is and the holding tank platform doesn’t seem so low to me so I was wondering if anyone had tried it.
Hi Ken,
I installed a holding tank on Ruby, a Parker 31, over the winter, and just as you suggest, to keep the plumbing as easy as possible, I used a gravity drain. It seems to work well. Obviously it is important to keep the drain pipe run as smooth as possible with as much downhill slope as you can manage.
I used one of the 25L tanks from Vetus, not cheap, suited the limited space available on a P31 very well. Of course the 31 has a higher deck, so I was able to mount it higher above the water line than might be possible on a 275.
Ted Sansom
Ted Sansom (P31/18)
Ken Surplice
HiTed, many thanks for your encouragement. I think I am going to have to do some measuring, there’s no avoiding it, to see how high, or low, my tank is relative to the waterline. I won’t say “wait for a rainy day” as we’ve had enough of those already. Cheers - Ken
chris nichols
Hi everyone,
while visiting Parkers some 12 years ago I had a look at a 285 which was having the deck fitted.
This model had a holding tank fitted under the Starborad deck behind the internal moldings. It was fitted on a bracket so it was high up, with just enough room for the holding tank pump out filler to fit along with the pipe from the loo. The sea exit was sited so it was an easy run to the waste out sea cock - thus making it relativly simple to clear any blockages by rodding from the pump out cap down to the seacock connection.

I fitted a similar system on our P27 along with an electric lavac loo. The tank was pattened using foam blocks which were trimmed to fit and placed on a 'shelf' grp'd to the side and main bulkhead. This allowed the positioning of the deck pump-out, side vent, pumped entrance and sea exit to be detremined. Standard Vetus fittings were used for these fitted to holes cut in the tank.
The tank was fabricated with grp as a hollow basin and seperate lid with these being fitted together with filled grp and many small s/s bolts. The whole was finished in white flo-coat.
All the electrics and the loo were concealed behind a replacement internal panel which fitted after the original grp molding had been cut out. a single button activates the pump and needs around 20 seconds of pumping to get a flow going.
It has worked well for the last 12 years providing around 30l of storeage (around 2 days for two people) and I have only had to replace the joker valves in the pump once. A single instance of blockage was caused by indigestable corn on the cob !
No smells and our day guests seem to be able to cope with 'flushing the loo' better than pumping.