Holding Tank Location

[HR]

We're in the process of rebuilding the head on our 40' ketch. We thought about installing an Airhead, but the two month delivery time doesn't work for our cruising plans, so we're reinstalling the Wilcox-Crittendon with a holding tank.

In Calder's book, he suggests that an ideal location for the tank is above the waterline thereby eliminating the need for a vented loop on the outlet side and a pump for emptying the tank in legal waters (since it can drain by gravity).

We have the space to do this and I was wondering if anyone has (or has seen) such an installation?

Howard

[mmd]

Yes. Did that on the Herreshoff Bounty project. Designed a tall, thin tank that spanned two frame bays and was suspended from the deckbeams above. It needed a check valve on the inlet side which always concerned me (what a miserable thing to clean if clogged!), but the owner never reported any trouble. I still believe that he is just lucky, and should have gone for my proposed piping layout where the inlet pipe was led to the top of the tank.

[Woxbox]

Our boat is set up that way. Never had a problem. It's a plastic catamaran, and the tank sits on the bridgedeck, actually under the cockpit seats to port. The inlet enters the top of the tank, and the outlet goes to a T valve -- one direction to the pump-out on the transom, the other direction to the overboard seacock.

It's not a big tank, and we're in the Chesapeake most of the time. So last year we added a Purasan unit -- so there's now a second Y valve at the top of the inlet loop. When not in an NDZ, we divert the line into that unit, which treats the waste and then drops it into the same overboard line that runs from the tank exit.

It may sound complicated, but it's proved 100% reliable and easy to use. We don't rely on check valves. The tank is vented, by the way, via a seperate small diameter line. The system gives us three options by flipping the two valves one way or another -- overboard, hold, or treat and overboard.

[John B]

I have friends who have set up their tanks that way and quite frankly, its a disaster of the stinking kind.They've had blockages, floods, raw sewage pumping out their vents , you name it.
As Michael says , you might be lucky, but to expect all that 'stuff' to run out as though it's water via gravity, well, when you think about it, its a bit of a big ask isn't it.
I agree that high and gravity assisted is the way to go because that keeps the system 'primed', but you need a pump to clear it so that there's no question of ever getting a block. After reading what the headmistress has to say the only variation I'd make to my system is to include 2 vents ( not one) so as to get some air circulation in the tank.That apparently improves the odour taint that they all seem to get.
Go the extra step and put a whale type toilet pump ( looks like a standard blige pump but is specially made for heads)in the tank exit line . peace of mind HR, peace of mind.;)

[mike hanyi]

all dufour yachts have them that way, one plastic tank per head and after delivering several of them I must say it is a great setup,

the inlet is from above, not below so the mess cant come back down the pipe, the dock pump out point just above it and the vent is also, of course there is a pipe under it with a thru hull attached.
emptying the tank is like filling it after visiting Kentucky Fried Chicken. instant!
it is also easy to clean the tank- open the seacock and force water into the deck pumpout, it runs right thru to get the peanut and corn bits unstuck!

great setup- go for it

[The Bigfella]

to get the peanut and corn bits unstuck


Gee thanks for that image Mike!

This is what I love about this forum - some great advice here. I've got this job coming up soon.

[HR]

Thanks for the comments - we're going to go for it. The tank inlet is at the top so that's not a problem. I'll keep in mind that we may have to add a pump if the gravity flow out doesn't work as well as expected.