Holding tank in the bilge?

[Peregrine1983]

Hi all,

We currently have a holding tank under our port settee. It's not big enough, and I am replacing the entire system because it's old and smells bad. All the hoses and the tank are going.

I am looking to install a larger holding tank. To fit a larger tank under my settee would require an L-shaped tank... Which I'm just not sure about.

The bilges on my boat are very big. Lots of dry, unused space under the cabin sole.

Is there any reason I wouldn't want to place the holding tank in the bilge under the cabin sole? The place I am thinking of putting it is high and dry above my keel, not near the sump of the bilge which is very deep and often has some water in it.

This location would be equidistant between my two heads, but the run for the vent hose would be longer as would the run to the thru-deck fitting for pumpouts. The run to the macerator pump through hull would be about the same.

Any thoughts appreciated!

[Orion Jim]

That's where my holding tank is. Perfect location....down low....still plenty of area left in the bilge for pumps, etc.

[Don C L]

I don’t know your boat but I don’t see why not. I briefly considered that with mine but my boat is much smaller and there was no good way to run the plumbing. Of course the obvious possible issue is that the tank won’t be emptied without a pump. I used to have a holding tank above the thru-hull that could be drained sans pump.

[Peregrine1983]

Thanks for the replies everyone. Yeah, I would have the macerator pump to pump it overboard - the macerator is actually a new addition. I do not currently have one.

The one thing I just realized is that my cabin sole hatches are only about 14"x14", so I'd have to do some sort of very long tank in order to not rip my floor out... and even then I'd have to make sure it makes the angle to get down there.

Looks like, unfortunately I'm stuck with going the L-shaped route if I want a bigger tank.

Don C L - I actually have thought long and hard about putting in two smaller holding tanks - one above and behind each head in the space between the hull and the cabinet. They would be above the waterline and thus drainable when I'm at sea. I just don't think I'd get the same amount of waste storage using the spaces behind the heads, and I'm worried the plumbing might be tight and complicated.

[Bill O]

Peregrine,
If I could make a few suggestions.
If at all possible use pvc pipe for your runs instead of the marine sanitation hose that will permeate after a few years and need replacement. We just replaced our hoses w/pvc and it was fairly easy.

Also instead of a macerator pump like this that will not work for too long before it locks up, get a more durable diaphragm pump. A little more expensive initially, but it performs much better and much quieter than the impeller pump. The impeller pump draws 16 amps compared to the diaphragm pump at 6 amps.


Bill O.

[Peregrine1983]

Thank you Bill. Just curious - are you referring to hard PVC pipe? Like what would be in a house?

[Tayana42]

I don’t know if this is any help but my holding tank (not mine, the boat’s) is in the bilge, under the cabin sole, about midships. Mine is a built in place fiberglass and plywood structure similar to my decks. Mine has a 35 gallon capacity. No reason not to by a ready made one if you find the right size and shape. Be sure to allow for flow under the tank for any actual bilge drainage. Also think about conduit for electrical runs you may have or want in the future.

[Dsanduril]

Originally Posted by Bill O

Peregrine,
If I could make a few suggestions.
If at all possible use pvc pipe for your runs instead of the marine sanitation hose that will permeate after a few years and need replacement. We just replaced our hoses w/pvc and it was fairly easy.

+1. Boats move enough that you probably need a bit of a flexible connection at both ends, but we're on our third boat with hard PVC pipe installed to the holding tank. For your bends search around and find "long radius elbows." You won't generally find them at Home Depot except in the lightweight DWV grades but you can find them in Sch. 40 or 80 at specialty shops.

[Bill O]

Originally Posted by Peregrine1983

Thank you Bill. Just curious - are you referring to hard PVC pipe? Like what would be in a house?

Yes and agree w/Dsanduril that you will need some flexible sections for the bends that are not available in pvc. Try to minimize the amount of sections as they will eventually need to be replaced in a few years.

Other thoughts I had after writing my previous post to reduce odors. Since you are building a new system make sure your new tank material isn't permeable (if using plastic) and your vent hose dia. is at least !"

We also switched from using seawater flushes to freshwater which helped reduce odor. Removing those dead crustaceans, etc. that more than likely added to the smell was worth the small amount of water usage from our tanks.

We did the pvc and freshwater head upgrades together, so somewhat hard to tell which one was the most beneficial. In the end, there isn't a whiff of head smell in the boat any more!

Bill O.

[Lepke]

Before electrics I used standard marine heads and always plumbed with schedule 80 plastic. Hard to break or damage. Any decent plumbing supply or irrigation company should have it. Also sweeping bends so it flows better.
One suggestion is put in a thru hull and drain so you can dump 3 miles out. Also add a fittings so you can flush the plumbing/tank with water if you have to fix a leak or replace a pump.

[Spindrift NH]

I have a 17 gallon holding tank located under the sole on my 424, it services both heads as well. It is not the original set up so I know it fit through the access hatch.

[FionaJC]

https://www.dropbox.com/s/best88mnq3...black.jpg?dl=0 This is a cross section of my tank area, I have a small black on Port and a larger grey tank on Starboard as close to the engine as the compartment allows. By using valves I can swich between pumping to sea or deck pumpout and I can select grey or black. They both vent through a vetus no-smell to the deck. The pump is a Whale gulper and I have a seacock. We dont actually use the black tank, its there if we need it though as we are in a tidal river basin. Its a struggle to get to the seacock but I can reach it. The valves are on the floor below the Nav desk. My drawing is more illustration than accurate.

[Smokeys Kitchen]

Bill O
Re: Holding tank in the bilge?
Peregrine,
If I could make a few suggestions.
If at all possible use pvc pipe for your runs instead of the marine sanitation hose that will permeate after a few years and need replacement. We just replaced our hoses w/pvc and it was fairly easy.

Also instead of a macerator pump like this that will not work for too long before it locks up, get a more durable diaphragm pump. A little more expensive initially, but it performs much better and much quieter than the impeller pump

+2 on all this. We rebuilt our head 1-1/2 years ago and have been very happy since. All hose replaced with PVC wherever practical, including any sweeping turns we could get; the rest with the best Trident we could get. New larger vent pipe/hose and straightened the run out. Went to a diaphragm pump so we would not have to worry about the pump running dry. Here was our choice; it even has a handle to turn it if the electricity goes out:

Lavatory Systems - Viking Power 32 & Viking Power Vacuum | Johnson Pump - Marine | Product Detail

Brand new holding tank from Ronco Plastics - well made and they will spin weld whatever fittings you want if you provide the specs.

For specific questions I'd email Peggy Hall on CF - she was a wealth of info for us and very helpful

Ron

[David B]

Originally Posted by Peregrine1983

Thanks for the replies everyone. Yeah, I would have the macerator pump to pump it overboard - the macerator is actually a new addition. I do not currently have one.

The one thing I just realized is that my cabin sole hatches are only about 14"x14", so I'd have to do some sort of very long tank in order to not rip my floor out... and even then I'd have to make sure it makes the angle to get down there.

Looks like, unfortunately I'm stuck with going the L-shaped route if I want a bigger tank.

Don C L - I actually have thought long and hard about putting in two smaller holding tanks - one above and behind each head in the space between the hull and the cabinet. They would be above the waterline and thus drainable when I'm at sea. I just don't think I'd get the same amount of waste storage using the spaces behind the heads, and I'm worried the plumbing might be tight and complicated.

Regarding your thought of two individual tanks behind the cabinetry in each head:
That's what we have, and the plumbing is very simple. Just a hose from the bowl macerator pump to the top of the tank, a vent line straight to the hull vent, a suction line straight to the deck fitting immediately above the tank, and of course a hose straight out of the bottom to the through-hull just under the wash basin. No pumping out, and the gravity dump takes all of 6-7 seconds (dock-side pump-out takes very little longer).

Regarding your thought of a new larger holding tank in the bilge area (lucky you to have a proper/decent bilge!), I suggest still having macerator pumps (therefore electric heads), so that what goes in the tank is readily pumpable when the time comes to empty, rather than macerating what is in there, on the way out. Also, a direct seawater inlet would be worth considering, so that you can flush the tank regularly.

[peghall]

For specific questions I'd email Peggy Hall on CF - she was a wealth of info for us and very helpful

I do try to be...and you're welcome to contact me directly.

Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein