Holding Tank Pumps

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fluffc

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Hi All,

Am looking to install a holding tank...

As well as the ability to pump out at a shore pump-out, I'd like to be able to pump out to the sea.

I'd like to have both an electric and manual pump for this. Reason being that normally I'd use the electric pump, but the manual as a backup.

If both pumps are diaphram pumps, logic would say that i could put one in series with the other. Has anyone done this? What problems have people found?

I think i would put the Manual pump first (nearest the tank), and then the Electric pump nearest the seacock.

What have other people done in this situation?


Shame i can't see how to do a questionaire any more on the forum. If i could, here are the questions:

Do you:

1. Rely on shore pump-out only
2. Have shore pump-out and manual pump to sea
3. Have shore pump-out and electric pump to sea
4. Have shore pump-out and manual + electric pump to sea


Should say that, boat is used for coastal sailing.
 
You haven't listed the option of "pump out to sea and no shore pump out", which I've seen quite often. However, my own boat has a fitting for shore suck-out, a manual pump to sea, and also the facility to pump out of the shore fitting using the boat's manual pump, which I'm not sure is useful (but was listed on the previous owner's envelope-back of valve settings). It's like a snakes' orgy in there.

I've not used an electric pump-out, but my electric bilge pump is a diaphragm one intended for waste and it claims that fitting in-line with a manual one is possible.

I haven't yet used the holding tank on this boat.

Pete
 
In ours:
Gravity pumps the tank out to sea (the tank is a few inches above sea level). The shore pump-out station sucks out the effluent. The only pump we have is the toilet pump, with a diverter either to sea or to the tank. It works well (only 18 months, but no blockages and quite a lot of use). Two pumps seems a bit over-complicated!
 
We have a holding tank with only electric pump out to sea.
The pump used to be a macerator pump which kept getting blocked. Current pump is a diaphragm pump which is much better.

If I had a choice I would have the toilet discharge straight to sea but currently it always goes via the holding tank.
 
I am thinking that having the toilet outlet permanently attached to the tank - ie can only pump to tank - would be the simplest for the 'users', and simplest to install.

But isthe added complexity of putting a valve in to switch between tank and sea really benficial?

Would consider it, if it's worth the hastle.
 
fluffc said:
1. Rely on shore pump-out only
2. Have shore pump-out and manual pump to sea
3. Have shore pump-out and electric pump to sea
4. Have shore pump-out and manual + electric pump to sea
Click to expand...

1. In the past seven years of full-time sailing for half of each year I have yet to see a pump-out station. I feel that my tank would probably be full by now;)

2. Unless the tank is going to be enormous this would be my option. I have some experience of seal failure on electric pumps and can vouch that washing electric motors full of poo is not enjoyable.

3. No.

4. Possible, but rather over-complex. Answering your original question, it is perfectly possible to fit them in series, the only draw back being that you will increase the system resistance. With positive displacement pumps this will not reduce the head available but it might increase the power requirement of the electric pump and the total flow rate.

As has been said, a gravity discharged tank is best if it can be arranged. I have this type, no diverter valves so everything goes through the tank. So far it has proved to be excellent.
 
fluffc said:
Hi All,

Am looking to install a holding tank...

As well as the ability to pump out at a shore pump-out, I'd like to be able to pump out to the sea.
Click to expand...

The correct design for the installation of an holding tank does not require any pump.
The holding tank must go above sea level. The toilet out hose goes into the holding tank from the top. The holding tank has a large drain hose connected from the bottom to a large drain seacock.

When in a marina the drain seacock is shut. During normal navigation the seacock is open which allows emptying of the hodling tank and flush through of the toilet waste.

A deck plug (same as water tank plug) is fitted on deck just above the holding tank with a water tank size hose connected to the top of the holding tank. This entry is used:

1) to insert the pumping out hose to pump out waste. Pump out services are normally supplied by a marina or at a fuel station
2) to flush and rinse the holding tank with fresh water to leave it in a clean state when not in use, in which case a fresh water hose is inserted on the top with the drain seacock open to flush.

ANY INSTALLATION UNDER WATER LEVEL OR REQUIRING A PUMP IS DESTINED TO GIVE LOTS OF SMELLY PROBLEMS. IF IN DOUBT, BETTER WITHOUT AN HOLDING TANK.
 
Last edited:
Several of you have commented about having the holding tank above water level. Is there an adverse effect on the stability of the boat when full?

I have a cavernous anchor locker - and could probably make use of the space above where the chain is; which is about 12" above the waterline.

I like the sound of a self-draining tank; just concerned about the stability issue?

I guess i shouldn't worry - boat weighs 10½ T, and has 2½ T of ballast...
 
Can't see stability ever being an issue, even if making the tank enormous. The biggest standard tank I can find on sale is 110 litres, although there may be bigger ones. So only the weight of a large man - would this affect your boat? You won't be doing much sailing with it anyway, open the valve when a couple of miles offshore.

We find our 50 litre tank to be plenty big enough for two people. Previously we had a 25 litre one that was OK, although it had a diverter valve so we only put solids in the tank.
 
My holding tank is about 3/4 below sea level and 1/4 above. There is an outlet with seacock, about 2 1/4 inches dia. which comes out of the hull at approx.45 deg.Once above 4kts the level in the tank drops by about 12inches sucked out by the motion of the boat thro. the water.(called something syphoning forgot the b---dy word) When in marina you can shut the seacock and use a pumpout when full.I always leave the seacock open but inspect the pipework regularly.Consequently the holding tank is always getting flushed out. never get any smells.By reversing the boat for some distance you can fully flush the tank out.Brilliant idea.
 
Haydude has it covered well. Gravity tanks are the way to go. Avoid pumps and below waterline tanks as they are all potential sources of trouble. Typical size is 40 to 70 litres and you will almost certainly need a custom made tank to make full use of the space. Pump out stations are almost non-existent in UK coastal waters, but it is worth having the fittings put in with the outlet directly above the outlet to the seacock so that you can access it for cleaning. Similarly, diverter valves are not really necessary - route everything through the tank. It is normal to try and get the inlet on the top, but one of my installations has the inlet at the bottom and an imternal stack.

Tek Tanks are the source for custom tanks and they will help you design your system. Lee Sanitation is another good source. Both have schematics on their websites.
 
fluffc said:
I am thinking that having the toilet outlet permanently attached to the tank - ie can only pump to tank - would be the simplest for the 'users', and simplest to install.

But isthe added complexity of putting a valve in to switch between tank and sea really benficial?

Would consider it, if it's worth the hastle.
Click to expand...

I had the tank / sea option when I installed my holding tank. Then the valve handle failed. Then it blocked. After a major clean up job (worse than I imagined it could be) - my toilet now only goes to the tank. I then manual pump to sea. No paper in the system - bagged for disposal ashore. I use a 'green' treatment to degrade the waste. Most of the tank contents is flush water anyway.
 
I decided on electric toilet straight into the holding tank.
Pump out is via a macerator pump just above the top of the tank so should be dry when not in use. This then goes out to the seacock via a standard vented loop.

No problems so far!
 
just had a tank plumbed in professionally by a yard i trust (Priors of Burnham).

Electric macerator pump installed as well as standard pump out access for shore installations to suck out. Diverter valve sends toilet waste either straight out of into the tank. Tank mainly above water line but not wholly. discharge through pump into a swan neck so gravity wouldn't discharge it anyway.

So, just hope all the horror stories above aren't true!
 
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