holding tank below water line

[bds]

Hi

I'm building a boat at the moment, and have got to make some decisions now about a holding tank. The consensus seems to be that a gravity system is the simplest and most likely to be problem-free, but unfortunately I really don't have room for a tank above the waterline (but have plenty of free/wasted below the waterline).

What I wondered is whether it is possible or sensible to implement the following system:

1. Toilet is a macerating type (already bought)
2. As with a gravity system, have all waste go via the holding tank instead of using a diverter valve
3. Have a float switch in the holding tank, that brings on a pump when there is anything in the tank. (Like an automatic greywater tank, but with the pump external)
4. Leave the pump 'live' while out at sea, switch it off while in port. (The seacock can even stay open except when the boat is unattended)

It is such a simple system and so easy to use that I suspect there must be a catch!! Can anyone enlighten me or, if it is a viable system, is it supplied anywhere as a kit?

Many thanks

 

[bobgarrett]

Having had a holding tank emptying failure I would recommend you do have a diverter so the toilet can always be used.
I would not recommend a float switch in the holding tank for "mechanical reasons". Nor is such an automatic option a good idea as it might come on at the wrong time. You need a gauge to indicate level and a manual switch to pump it out.
Don't forget a deck outlet too so that when in an area where you are not allowed to dump at sea you can pump it out.
I'd assume http://www.leesan.com/ will have all you need.

 

[Carmel2]

You don't need a float switch, rap your knuckles on the tank, you will know when its time to dump, also +1 for a Jabsco Y valve.

 

[boatmike]

When pumping Poo it's important to keep it simple. On my boat I have a holding tank that is indeed below the waterline. In my opinion the ideal place for it. The toilet discharges directly into the tank and the discharge is through a whale gusher manual pump that is ABOVE the waterline so that it can easily be maintained. The outlet of course is below waterline. There is also an overflow in the top of the tank that also discharges below the WL but with an anti-syphon loop above the WL and a separate sea cock just in case I forget to pump out or anything goes wrong with the pump that cannot be dealt with immediately. This avoids the necessity for a diverter valve. Of course this is only one way to do it. Some will prefer to have the overflow above the WL to act as an air vent (which of course you will also need) and avoid another sea cock, but it ain't gone wrong yet! Hope this helps.

 

[bds]

Thanks to all who have responded. I have a few responses and more questions now:

Having had a holding tank emptying failure I would recommend you do have a diverter so the toilet can always be used.

Good point. I could add a manual backup pump as a first line of defence, but if all else fails there is always a bucket or a tree/pub depending on where I am!

I would not recommend a float switch in the holding tank for "mechanical reasons".

This is interesting - can you expand on this? Is it still a problem even though the poo is macerated? I'm genuinely asking as I have no experience of these gizmos

Nor is such an automatic option a good idea as it might come on at the wrong time.

No problem here - my sea vs port switch would isolate the pump completely so it couldn't operate in port (unless I forgot to flip the switch, but then again, one could just as easily forget a seacock or y-valve)

You need a gauge to indicate level and a manual switch to pump it out.

Why is a gauge less vulnerable than a float switch?

Don't forget a deck outlet too so that when in an area where you are not allowed to dump at sea you can pump it out.

Another very good point, but would apply to any system - I'm keen to establish the basic system first.

You don't need a float switch, rap your knuckles on the tank, you will know when its time to dump, also +1 for a Jabsco Y valve.

Unfortunately the tank is very remote from the toilet, and inaccessible without removing watertight inspection panels. For that reason I really want to avoid the Y valve, because I either have to run miles of piping to a common seacock (tank and direct discharge), or have an extra one, both of which I want to avoid.

When pumping Poo it's important to keep it simple. On my boat I have a holding tank that is indeed below the waterline. In my opinion the ideal place for it. The toilet discharges directly into the tank and the discharge is through a whale gusher manual pump that is ABOVE the waterline so that it can easily be maintained. The outlet of course is below waterline. There is also an overflow in the top of the tank that also discharges below the WL but with an anti-syphon loop above the WL and a separate sea cock just in case I forget to pump out or anything goes wrong with the pump that cannot be dealt with immediately. This avoids the necessity for a diverter valve. Of course this is only one way to do it. Some will prefer to have the overflow above the WL to act as an air vent (which of course you will also need) and avoid another sea cock, but it ain't gone wrong yet! Hope this helps.

Sounds like a great system, but I would really like to avoid manual pumping every time someone uses the loo. Overflow issues should not be a problem - with the electric loo, it won't flush when the tank is full.

Is there anything else I am not seeing?

All comments gratefully received!

 

[rotrax]

When pumping Poo it's important to keep it simple. On my boat I have a holding tank that is indeed below the waterline. In my opinion the ideal place for it. The toilet discharges directly into the tank and the discharge is through a whale gusher manual pump that is ABOVE the waterline so that it can easily be maintained. The outlet of course is below waterline. There is also an overflow in the top of the tank that also discharges below the WL but with an anti-syphon loop above the WL and a separate sea cock just in case I forget to pump out or anything goes wrong with the pump that cannot be dealt with immediately. This avoids the necessity for a diverter valve. Of course this is only one way to do it. Some will prefer to have the overflow above the WL to act as an air vent (which of course you will also need) and avoid another sea cock, but it ain't gone wrong yet! Hope this helps.

The standard system on Island Packet Yachts is similar but with a 12v Jabsco macerator pump. Our tank is in the bowels of the forepeak, lying on the bilge and is 40 US gallons-160 litres.

The only service required in six seasons was servicing the diverter valve-it got really stiff.

 

[Sarnia]

Having had a holding tank emptying failure I would recommend you do have a diverter so the toilet can always be used.
I would not recommend a float switch in the holding tank for "mechanical reasons". Nor is such an automatic option a good idea as it might come on at the wrong time. You need a gauge to indicate level and a manual switch to pump it out.
Don't forget a deck outlet too so that when in an area where you are not allowed to dump at sea you can pump it out.
I'd assume http://www.leesan.com/ will have all you need.

Agree with all of that, took advice at Tektanks, who have lots of diagrams of setups, they did one for me from the measurements I gave them below the waterline. www.tek-tanks.com
I built my own tank from marine ply, full epoxy treatment inside, again with pro advice from our resident Australian epoxy expert here. Made it to fit under one of my forward bunk spaces. In the top of the tank I fitted an inspection hatch, 6" dia. and a deck pump out fitting, access to it via a hatch over the forward compartment, so easy to get a pipe on to it if required. (didn’t' want to fit one in my teak deck)
My head still has its original Henderson manual pump in situ, but not connected as heads updated with Jabsco.
Tested the Henderson worked perfectly as pump out, fitted a 3 way valve, which directs from head to the tank when required, or to the Blakes.
Outlet has an isolator valve in line and connects to a Y fitting at the Blakes thru-hull. A breather fitted well above waterline, the only extra thru-hull required.

 

[boatmike]

Agreed. You can use the system I described with a manual or electric pump and/or a manual or electric toilet. The point is that you don't need diverter valves or complications like float switches etc. If you forget to empty the tank you can still use the toilet and it simply pumps through the tank and overboard through the overflow pipe. Of course we always remember to pump out at sea don't we........ so no worries! What you don't want with any system is anything that would allow the poo to stagnate and solidify so a system that always discharges into the tank is an advantage. You also of course can pump clean seawater using the toilet to flush the tank which you should do before leaving the boat for any length of time which avoids build up. Avoid anything inside the tank other than poo..... Do you really want to be opening up the tank and delving about inside to free up a stuck float valve????

 

[rogerthebodger]

What ever you do just make sure that all the piping can be removed easily when, not if, it becomes blocked.

 

[rotrax]

What ever you do just make sure that all the piping can be removed easily when, not if, it becomes blocked.

Once these pipes are replaced, leaving white vinegar in the system when the boat is left keeps the bowl and pipes clean.

I have just purchased 4x5 litres from EBAY-its cheap.

About 2-2.5 litres put down the bowl and pumped through untill it is level with the normal dry bowl level works for us. It fizzes gently away . I read on another site that a 2 litre bottle of coke does the same.

 

[rogerthebodger]

Once these pipes are replaced, leaving white vinegar in the system when the boat is left keeps the bowl and pipes clean.

I have just purchased 4x5 litres from EBAY-its cheap.

About 2-2.5 litres put down the bowl and pumped through until it is level with the normal dry bowl level works for us. It fizzes gently away . I read on another site that a 2 litre bottle of coke does the same.

We used to do that every time we left the boat and I have also cleaned a henderson pump with white vinegar. The pump did come clean soaking in a bucket for 2 weeks replacing the vinegar when it stopped. IMHO white vinegar is not strong enough and where the pipe is below water line the vinegar gets diluted to a point where it is of little use. I used hydrochloric acid and what I think happened was the acid caused some of the calcium to soften and break off causing the blockage.

The best way I found is to remove the pipe and beat six sh1ts out of it on the walkon to dislodge all the crud.

 

[BabaYaga]

Unfortunately the tank is very remote from the toilet, and inaccessible without removing watertight inspection panels. For that reason I really want to avoid the Y valve, because I either have to run miles of piping to a common seacock (tank and direct discharge), or have an extra one, both of which I want to avoid.

If the distance between toilet and tank is very long, you will be pumping a lot of water just to flush (or will be leaving waste standing in the hoses). Therefore the tank will have to have a larger volume to give the same capacity of 'average number of uses to fill the tank', compared to if the toilet and tank were close by.
Unless your tank is really large, my advice would be to reconsider if a diverter valve and an extra seacock by the toilet is really such a disadvantage.
The overflow approach suggested by boatmike is interesting. But I can think of situations with a full tank where using the toilet with a direct discharge still would feel socially acceptable and discharging via a tank overflow less so.

 

[Sinbad1951]

Love the idea of having TWO electric pumps in the poo system on your boat. lol. That way you can guarantee you wont be doing any sailing, just fixing.
The ideal solution is to manually pump up to a holding tank above the waterline which you can empty by gravity. If you have to have a system with an electric pump have one only and make sure its function is to empty the holding tank. Avoid macerator pumps like the plague. Its only a question of time before a tissue or a piece of dental floss or some non digested fibre clogs up the cutter. Install a proper poo pump. I would suggest you spend a £100 quid more than you thought and get the Sealand T series vacuum pump. No macerator just suction alone. Place the pump in a place where you have easy access to both the pump and the pipework connections to the pump. If possible make a small part of your pipe run considt of clear pipe. That way you have the option to check visually to see if the pump is emptying the holding tank.
Lastly, get the holding tank made from semi opaque plastic. You can check the levels by looking at it. Do everything you can to avoid having to sit or crouch in a restricted position trying to get a pump working when its full of sh**. Its no fun. Ask me how I know all this.........

 

[Quandary]

Our last boat was a Finngulf, a respected Finnish marque, who did not cut any corners, the holding tank occupied the otherwise useless void below the floor of the cockpit locker immediately behind the head and below the water line. The loo pumped straight into the holding tank, no diverter valve, well above the tank on the bulkhead between the head and the locker there was a Henderson pump discharging via a loop to deck level back down through a seacock in a low level locker under the wet gear space beside the loo. The handle for this pump was above and outboard of the bowl in the head. The vent from the tank rose from the top to deck level and then down to a manifold under the transom. The shore pump out pipe rose straight from the tank up the back of the locker to a filler cap on the side deck. In port the loo was pumped into the tank, once at sea the Henderson pump handle was used to clear the tank, coming up to the end of a trip the Jabsco loo pump was used to put more water in the tank then flushed out with the Henderson. Simple robust and effective with little to go wrong and only one seacock.
There was only one occasional problem, when we were sailing fast the stern wave rose to cover the manifold, effectively blocking the vent outlet, the vigorous motion agitated the contents of the tank which then vented back through the loo pump, creating a smell in the head compartment. We switched to one of those 'twist to lock' pumps which mitigated it but the best cure was to pump out and preferably flush the tank early in a long vigorous fast sail. With the pump out handle located above the pan this became routine. Re-positioning the vent a bit higher would have cured it completely but once we were aware it was easy enough to avoid the problem, in eight years of fairly heavy use we had no other problems so I support those who recommend keeping it simple (and manual).

 

[Birdseye]

Hi

I'm building a boat at the moment, and have got to make some decisions now about a holding tank. The consensus seems to be that a gravity system is the simplest and most likely to be problem-free, but unfortunately I really don't have room for a tank above the waterline (but have plenty of free/wasted below the waterline).

What I wondered is whether it is possible or sensible to implement the following system:

1. Toilet is a macerating type (already bought)
2. As with a gravity system, have all waste go via the holding tank instead of using a diverter valve
3. Have a float switch in the holding tank, that brings on a pump when there is anything in the tank. (Like an automatic greywater tank, but with the pump external)
4. Leave the pump 'live' while out at sea, switch it off while in port. (The seacock can even stay open except when the boat is unattended)

It is such a simple system and so easy to use that I suspect there must be a catch!! Can anyone enlighten me or, if it is a viable system, is it supplied anywhere as a kit?

Many thanks

Not necesary to be so complicated. I made and fitted a holding tank to a previous boat. The emptying system had a pick up pipe going through the top of the tank to within an inch of the bottom, up in a loop and then to a seacock via a diaphragm pump. All the pump did was to start up the syphon but once the syphon was broken the tank didnt empty. Simple and totally reliable

The advice I got and which worked well was to plumb the system in abs domestic pipe. All flexible pipe has plasticiser ( key to making it flexible) which makes it ever so slightly porous and gives rise to smell over time.

Made sure that there was a removeable inspection hatch. Decent diameter air inlet with an anti pong filter on the end.

Golden rule - no toilet paper down the loo. Instead it went into a plastic bag in a pedal bin. I was afraid that it would smell but it didnt at all.

 

[Sarnia]

Agreed. You can use the system I described with a manual or electric pump and/or a manual or electric toilet. The point is that you don't need diverter valves or complications like float switches etc. If you forget to empty the tank you can still use the toilet and it simply pumps through the tank and overboard through the overflow pipe. Of course we always remember to pump out at sea don't we........ so no worries! What you don't want with any system is anything that would allow the poo to stagnate and solidify so a system that always discharges into the tank is an advantage. You also of course can pump clean seawater using the toilet to flush the tank which you should do before leaving the boat for any length of time which avoids build up. Avoid anything inside the tank other than poo..... Do you really want to be opening up the tank and delving about inside to free up a stuck float valve????

The KISS principle: Keep It Simple Stupid works every time

 

[bobgarrett]

As others have suggested, things will fail so design must take this into account.

A float switch will fail, maybe on and maybe off. So automatic switch is a bad idea. A gauge suggesting when to switch on is better.

A pump will fail so pumping out through deck is essential or fixing the pump will be even messier.