Pump up -gravity out holding tanks

[swagman]

One last tip.
If you are building a gravity tank make sure the deck outlet (used to pump out if you ever find a shoreside pump facility) aligns perfectly with the gravity exit (through hull).
That way, if someone does ever deposit something not degradable into the tank you can use a long rod to poke from the deck downward and push the offending item out, as opposed to having to dismantle anything.
It beats trying to suck it out!
JOHN

[GordMay]

Originally Posted by swagman

One last tip.
If you are building a gravity tank make sure the deck outlet (used to pump out if you ever find a shoreside pump facility) aligns perfectly with the gravity exit (through hull).
That way, if someone does ever deposit something not degradable into the tank you can use a long rod to poke from the deck downward and push the offending item out, as opposed to having to dismantle anything.
It beats trying to suck it out!
JOHN

A 25' (< $15) -to- 50' (<$40) Steel Fish Tape is a very useful tool to have aboard.
Also available in S/S & Fibreglass, at higher prices.

[donradcliffe]

I'd recommend against a gravity tank for two reasons:

1. Too much back pressure against the joker valve is not a good thing--you REALLY don't want the contents of the holding tank to fill the toilet bowl, let alone overflow it.

2. While not likely with 1 1/2 inch hoses, the outlet of the tank can get clogged (after one experience I now religiously flush the toilet and pump again after emtying the tank), and a self-priming pump on the outlet gives you a bit more pressure to push the clog through.

[Beausoleil]

Originally Posted by donradcliffe

1. Too much back pressure against the joker valve is not a good thing--you REALLY don't want the contents of the holding tank to fill the toilet bowl, let alone overflow it.

That wouldn't be a problem if the inlet to the tank is at its top rather than at the side. Then what you essentially have is a vented loop, and only the contents of the hose could possibly leak back into the head - same as a standard vented loop.

I'll be finishing a similar installation tonight. The added kicker is that we'll have the option of a Raritan Electro-Scan to treat the effluent before it goes into the holding tank. Normal operation will have the holding tank outlet open so the treated effluent just flows right on overboard. We'll close the outlet valve on the tank when in No-discharge Areas, which seem to be becoming common here in the States.

A bit off-topic: A couple of weeks ago I heard an interview on NPR with one of the environmental backers of No-Discharge areas in Massachusetts. He served up what I believe to be a blatant lie to the interviewer by saying that No-Discharge areas will prevent the discharge of untreated waste into local waters, making it sound to the average non-boating listener that it was a good thing to do. And just how many non-boating listeners to the interview knew that it's already illegal to discharge non-treated sewage within a 3-mile limit throughout US waters? I just can't believe it was an honest mis-statement. They want all discharge - even that of a Type-I MSD - go be illegal.

[Roy M]

Here is my holding tank installation on a Searunner 40 tri. The head is in the forepeak (foredeck hatch above, heavy duty lid above toilet for working headsails in heavy weather). The tank uses two 1 1/2" vent hoses led to each side of the bow, following the concepts of Annie Hall's aerobic digester design (uses aerobic bacteria to process waste - great idea!). The waste enters from a Lavac toilet, via a Whale 10 bilge pump (which thoroughly macerates paper and waste), and enters the tank from above. There is also an inspection plate, should an eager ICE inspector wish to confirm I had no drugs or illegals hidden there. Waste flows by gravity to the lower hose (with a tee for a deck cleanout port), then through a plastic ball valve (lockable in closed position) then overboard at the boottop. The only moving parts are the lids, the pump handle, the three rubber parts in the Whale bilge pump, and, of course, the ball valve handle. No electrics or significantly maintained systems. The big black stacked pumps on the left are the saltwater deck washdown pump (using the head's seawater intake throughhull).

[Catamount]

Here's a pic of my recently installed gravity-drain waste holding tank:



I built the tank myself from recycled fiberglass panels.

The top of the tank is recessed about an inch below the top of the tank walls, creating a flange that was used to secure the tank to the bulkhead, and which will contain any leaks from any of the fittings. These include (from left to right) the pump-out dip tube, vent, access/view port, and inlet fitting.

The pump evacuates a Lavac Popular marine toilet. The valve on the bottom connects to the discharge seacock. The bottom of the tank is just above the waterline. Sailing hard on the wind on a starboard tack with the valve and seacock open should generate plenty of cleansing action!

Access/View Port? Why would anyone want to see into their holding tank? But I believe the regs require some means of monitoring the tank level -- with a clear insert screwed into the access port, I can shine a flashlight and see just how full the tank is (or isn't).


Here's a view into the tank, where you can see the pump-out dip-tube tabbed to the side of the tank, and the internal baffle that I installed.



I can tell you from experience so far that the system works really well!

[vacendak]

I studied this picture thoroughly



© Jim Soilers

cannot imagine where to find appropriate place for e.g. 100 ltr holding tank

[James S]

Nice work you guys!!

[Ti' Punch]

Hey all,

I don't know if anyone is still following this thread, but I've got a problem that I believe is closely related. I have a catamaran with the holding tank mounted in a foredeck locker between the hulls. This was installed by the PO and appears to me to be a token gesture towards complying with the discharge laws. There is no vent line and the tank appears to never have been used. We spent the first season on the boat using a porta-pottie because I wanted to sail the new to me boat and not worry about projects, BUT, the Admiral is now insisting that she be able to use at least one of the two heads onboard during season two.

I was contemplating how to make this system functional when I stumbled on this thread. The thing I'm struggling with is that with a single tank mounted amidships in the foredeck locker, I end up with discharge lines from each head that are about 10' long with about a 4' rise from the head discharge to the tank inlet. This seems to me like there would be a lot of standing water, or worse, left in these long discharge lines after a flush. Reading this thread reinforces my fears now with the comment about backpressure on the joker valve being an issue. I suppose I could put in a check valve at some point, but that seems like I'd just be asking for a clog.

So, now I'm thinking maybe I should go with two smaller tanks mounted above each head. Both heads have existing overboard discharges with Y valves going to the holding tank, so the gravity drain method would work. I'm not keen on cutting two new holes in the deck for pumpouts. I could probably get by with a holding tank on one side and then just put a locking valve on the other head discharge for when we are inshore, or maybe I could run lines from the two tanks to the single existing deck pumpout fitting in the bridgedeck and just use a Y valve to select which tank I'm pumping. Basically, I'm paralyzed by the options right now. Opinions?

I hate long posts, so my sincere gratitude to anyone that made it this far. --- Chris

[Roy M]

Chris, Is your head located in the bows of the cat? Is there a space forward? In many cats there is a crash bulkhead separating this deck-accessed locker from the forwardmost cabin space. You could install an underdeck holding tank in that compartment and keep the hose short, assuming the head is adjacent to the crash bulkhead.

If not, you may be SOL. You are absolutely correct about the "drop-back" from the toilet bowl to the loop rise of the discharge hose. If you give extra pumps to get the crap over the loop, only clean seawater will remain in the loop, but it will fall back to the bowl, and if too long, fill the bowl excessively.

[Ti' Punch]

Roy,

Unfortunately, I think I'm SOL. The heads are located amidships in both hulls separating the fwd and aft cabins. What do you think about putting in two smaller tanks closer to the heads with gravity drains going to the existing overboard discharges and running both pumpout lines to a Y valve at the existing deck pumpout? The pumpout lines would be long, but that shouldn't be a problem I don't think. Sound reasonable?

Thanks for the reply --- Chris

[Roy M]

It sounds do-able to install smaller tanks, but that is a judgement call on your side as to how much space you are willing to sacrifice, and where the tank would be located. As for the pumpout hoses, again, your call. You know your boat and you know what compromises and sacrifices you are willing to make. I would tend to go with independent pumpout locations to keep the plumbing short and simple. Heads are usually pretty cramped areas with little available real estate for holding tanks of any size. I imagine your daggerboard trunks are adjacent to them, also reducing potential locations. Maybe, if you have a shower, you could create a seat that contains the holding tank?