Plumbing / tank pumping question

[Cormorant]

I'm getting ready to install a head on our boat (a 31' homebuilt Michalak Cormorant). Our first real head, after four years of summertime cruising! Up till now we've made due with a series of lovely 5-gallon pails in a wooden box with a toilet seat on it, and cedar cat litter in the pail. 'Nuff said about that. . . .

In the interest of keeping it simple and keeping costs manageable, I'm leaning toward a manual Raritan PHII, pumped to a holding tank, with the option to pump the holding tank overboard, or have it pumped out at a shoreside facility. No need for direct discharge from the head overboard, as we don't really spend long amounts of time offshore.

So I found this diagram in Don Casey's article "Installing a Head" on boatus.com. I like his layout, but then it occurred to me that we could save the cost of the extra diaphragm pump if we used pressure from the toilet pump to evacuate the holding tank. I'd need to install a cutoff valve in the tank vent line (possibly dangerous if I forget to reset it to open).

If it matters, the tank would be about one half above the waterline and one half below. Rim of toilet will be about 7" above waterline. I'm going to try to attach Don Casey's diagram as marked up by me.



So, can I skip the separate diaphragm pump, close the tank vent, switch the tank's Y-valve to the through-hull, and use pressure from the toilet to push the tank contents out? Would this work? Am I just being a ridiculous cheapskate? It's also a simplicity / space-saving thing . . .

Thanks for any advice!

[Hud3]

There's another thread about smelly leaks from a holding tank. The problem was solved when the plugged vent line was cleared. I'm not sure I'd plug it (with a ball valve) on purpose!

http://www.cruisersforum.com/forums/f115/horrible-odor-from-head-help-please-22884-2.html

[44'cruisingcat]

Originally Posted by Cormorant

So, can I skip the separate diaphragm pump, close the tank vent, switch the tank's Y-valve to the through-hull, and use pressure from the toilet to push the tank contents out? Would this work? Am I just being a ridiculous cheapskate? It's also a simplicity / space-saving thing . . .

Thanks for any advice!

No, it wouldn't empty the tank. You're trying to displace the water in the tank by pumping more water into it. For every litre you push out, you'd have to pump a litre in.

It would work without needing a discharge pump if the tank was high enough that gravity would empty it though, by swinging the Y valve and leaving the vent open.

[Cormorant]

For some reason I had the impression that the PHII could be set to dry-pump the bowl and send only air into the line. That was the basis of my whole crazy scheme. I take it that's not the case. . . .

Thanks!

[44'cruisingcat]

Maybe it can, you would need to check with Raritan. The manual toilets I've had wouldn't have.

[Cheechako]

Looks like the system that Hallberg Rassy has used for years, although their tank is above the waterline completely I believe. If you can keep the outlet hose from the bottom of the tank to the thru hull short, the tank should gravity drain when the hull valve is opened. Your tank is a few inches below the water line, so you may need boat movement to suck the last out. Keep the vent open. You dont even need a troublesome Y valve. just use a T to the deck fitting and the thru hull to shut flow from going overboard! Make the overboard flow as straight a shot as possible.

[rtbates]

You might take a look at LAVAC heads. They use a external Henderson pump that, with a few Y valves, can be used to pump out the tank. They are also wonderful heads. The Henderson pump is a diagraph type that can pass a tennis shoe... It beats the heck out of the tiny piston pump in most heads.

[Cormorant]

I've thought about the Lavac a lot. (I spend too much time thinking about my boat's future toilet when I really should be working.) I could still go either way.

I think the cons of Lavac were:
-- non-intuitive mode of operation might flummox guests
-- reported problems with seat gasket
-- 2-minute wait after flushing till toilet can be opened
-- parts available only from a few places
-- hmm . . . I thought there was another con . . .

Pros for the Lavac were:
-- tennis-shoe swallowing
-- simple mechanism, less to go wrong
-- can use diaphragm pump as emergency bilge pump
-- vacuum flush possibly has a slight macerating effect without a macerator
-- many many happy customers

Pros for the PHII went something like:
-- more "normal" mode of operation, might be more guest-friendly
-- reliable pump with many happy customers
-- parts readily available in many places
-- could probably rig the toilet intake as an emergency bilge pump if I had to . . .

Cons for PHII:
-- various reports of rebuilds, clogs, etc., but not enough to make it sound bad

Somehow, for now, I've landed on the PHII, but am always open to new advice and opinions.

[Tempest245]

Originally Posted by Cormorant

pumped to a holding tank, with the option to pump the holding tank overboard, or have it pumped out at a shoreside facility. No need for direct discharge from the head overboard, as we don't really spend long amounts of time offshore.

This part puzzles me a little....I don't see the difference between a direct overboard discharge and a holding tank to overboard discharge.
Or should I say, the purpose of holding it..just to dump it overboard.

Why not just put the " Y " valve before the Tank...divert it overboard, or divert to the tank. If you are in regulated waters, the handle needs to be locked, or removed with the flow to the holding tank. When you go offshore, you can divert directly overboard...

I'm sure there's something I'm missing.

[fastfilm]

The Don Casey diagram is essentially the system on my Tartan 30. It works great. Looking at my system, gravity drainage of the tank (as I have encountered on a couple of new charter boats) was not possible due to location of the holding tank and the apparent desire to use the existing through-hulls from its original pre-holding tank installation. A big whale tail pump can empty my tank in a hurry. Pay attention to routing your lines in order to prevent stink from the tank feeding back into the cabin.

[Cormorant]

Originally Posted by Tempest245

This part puzzles me a little....I don't see the difference between a direct overboard discharge and a holding tank to overboard discharge. Or should I say, the purpose of holding it..just to dump it overboard.

We spend most of our time in near-shore coastal waters (can't flush directly overboard).

But I'd like to have the option to empty our tank in open water when necessary.

I don't want to be forced to a shoreside pumpout station if it's only for that. I'd rather time our visits to civilization based only on the need for ice cream.

Really I'm imagining a two-month Bahamas trip. We can hold waste in the tank when in a harbor or near a beach, etc. The tank will probably hold about 7-10 days' waste for our family of four. Sometime each week we'll make a passage to a new island or, say, from the Berries to Nassau, and empty the tank.

No need to go to a pumpout station.

We also do a lot of cruising in the Cape Cod / MV / Nantucket area (1-2 weeks at a time), and I'd like to have the same flexibility there.

[Tempest245]

Ok.....sounds like everything goes overboard.

[Boracay]

The "cons" of the Lavac were:
-- My guests either have no problems or refuse to use the head.
-- I have not experienced any problems with the seat gasket. Continued "close" inspection is recommended.
-- I find I can lift the seat against the vacuum after a few seconds. I'll time it next time.
-- parts not normally needed. My manual bilge pump is also a 1.5" Henderson. I'll probably buy another as spare.

"Pros" for the Lavac were:
-- my Lavac quits if I use three ply toilet paper. Very unpleasant experience.
-- simple mechanism, less to go wrong (really hard to stuff up, but I've managed).
-- If the water gets above the toilet bowl I don't think that I'll be using the Lavac.
-- vacuum flush has a major macerating effect.
-- many happy customers (+1)

If your holding tank is really half below the water line than I would strongly recommend using a pump to empty it. The Henderson MkV comes to mind.

[Cormorant]

I think the other "con" of the Lavac was: I had read about it not leaving the bowl sides clean all the time, requiring a scrubbing with a toilet brush after use sometimes. Not sure if this is something the Lavac experiences more often than any other head. . . .

In any case, Boracay, I appreciate your report. That macerating effect counts for a lot, I think.

[Cormorant]

Going back to my original question about using pressure from the toilet pump to evacuate the holding tank, I posed the question to Vic at Raritan, just to clarify whether the PHII pump could be pumped "air only." Here's his reply. (I'm so impressed with the level of detail he gives to prospective customers. Really a shock in this day and age. . . .)

---------------------

I can definitely appreciate your ingenuity, and the "modified" plumbing the
system as you described will probably work for a while. But it wouldn't be
suitable on an ongoing basis. As the rubber seals in the toilet's pump
begin to wear, you'd get a lot less pressure on the discharge of the toilet,
and at that point, it wouldn't work any longer.

The internal parts of the toilet pump depend on the water being pumped to
lubricate them. Pumping the toilet "dry" for extended periods will
accelerate the wear of the internal parts of the toilet, particularly the
piston "O" ring, which is hollow inside; it is not solid rubber. The square
cross section of the "O" ring is rather thin, and if it wears through, the
head won't pump any longer - until the "O" ring is replaced, which involves
disassembling the whole pump.

So, if it were I, I'd stick to the original design. But your idea is
intriguing, and I will pass it along to our engineers for their info.
----------------------

It occurs to me that I could pour in a cup of vegetable oil just prior to each dry-pumping to avoid wear on the O-ring. But really, we're talking here about me trying to avoid buying a $50 diaphragm pump. . . . I'm an awful cheapskate, and I enjoy trying to pinch pennies via pure functionality . . . but it's not worth the risk to the system. I'm getting the extra pump.