We are doing a final install on a new head system and have hit one area where we can't make a final decision due to competing suggestions, so we hope the resident expert can weigh in. First, , the head bowl and top of the holding tank are above the static waterline, but both could be below the waterline when the boat is on starboard tack. Water supply for the head will be from a small, dedicated fresh water tank located under the (this eliminates at least on vented loop). We went with a very simple system where the head (PHII) discharge runs about four feet horizontally to the top of the holding tank, with a slight rise mid-way to prevent any backflow from the line into the head. Another line runs vertically from the bottom of the holding tank to the deck pump out. For emptying the tank at sea, we were going to install a 3-way valve on the vertical hose to the pump out fitting. That valve could be installed above the static waterline, but would have the potential to be below the waterline during extreme healing situations on starboard tack. From the 3-way valve, a discharge hose would descend to the overboard discharge thru-hull, with a Whale or similar manual pump somewhere in that line. The question is with this set-up, could we forego a vented loop on the discharge line to the thru-hull? The reasoning being that (a) the line between the thru-hull and holding tank would rise above the static waterline (with the 3-way valve always being above the waterline when pumping out at sea), and (b) the thru-hull would only be open when actively pumping out the tank when offshore. Looking for thoughts on this particular set-up . . .
Vented Loop
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Your setup sounds a lot like mine, with the head discharging directly to the holding tank and a diverter valve in the pumpout line that allows you to dump the tank. IMHO, since you have both the diverter valve and the seacock, you shouldn't need to have an anti-siphon loop in the discharge line. I'm sure Peggie will chime in shortly.
I'd point out that the Whale diaphragm pump will also act as a check valve...since it has two check valves in it as part of its design. So that makes three things keeping the seawater from flowing back through the holding tank discharge line—the seacock, the Whale pump and the diverter valve.
I'd point out that the Whale diaphragm pump will also act as a check valve...since it has two check valves in it as part of its design. So that makes three things keeping the seawater from flowing back through the holding tank discharge line—the seacock, the Whale pump and the diverter valve.
Not necessarily. No...you can't sink the boat. But if the toilet is left in the "flush" mode, you can drain the flush water tank if there's no vented loop in the system. There are also easier ways to do it than a dedicated flush water tank.
A slight rise may or may not be enough. You wouldn't need any rise if your inlet fitting on the tank were located on the inboard side of the tank instead of outboard. If it is outboard, you'd need a loop--not necessarily vented, just a loop--as high as a vented loop to prevent backflow.
No. You'd never get that past an insurance survey.
The reasoning is sound, but it doesn't allow for human fallibility...for the possibility that SOMEONE--maybe you, maybe a future owner--could leave the thru-hull open for "convenience." There's far more of that these days than there used to be or should be.
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Thanks Peggy and SD. Peggy - how do you think we could simplify the intake side? We haven't installed the flush tank, yet, so could easily make a change at this point.
As for the survey, that was one of our concerns. Like SD noted, there are lots of redundancies in the system - that means it would be very safe for us (unlilke most of our dockmates, we are always vigilent about closing seacocks both when away from the boat and when we are not using the attached plumbing), but I don't want to have to pull it appart and rebuild for the next survey. That said, we will install a vented loop at the high point upstream from the discharge pump.
The simplest way to get the head to flush with fresh water is to tap the head intake off the sink drain line, assuming that the sink drains below the waterline. If you plug the sink drain in the bowl, and leave the seacock open, the head will flush using salt water. Close the seacock and pour water in the sink and it will flush using fresh water. Gives you the best of both worlds with a very simple modification and eliminates the need for a separate through-hull and seacock for the head intake.
Yes, I considered that option, but we have frequent guests on the boat and I figured it would be a bit more complicated to explain the process to people who are not already familiar with a marine head. If it were just my wife and I most of the time, I'd probably go that route. Instead, we are considering installing a small 3 gal. tank that would be dedicated to the head intake and put it in a location where it could be easily refilled - probably under the sink or in the bilge just below the head.
Gee, unless you use the sink in the head all the time, then just have it set up closed and ask them to wash their hands in the galley sink. KISS. A separate tank for a head makes so little sense... And, alternatively, if you follow the logic, use the sea water all day and just use the sink for the end of the day cleanout of the hoses that go to the head, which is where the smells come from.
There is no process...
There is no "process" to using a toilet connected to the sink drain. The only instructions needed in addition to the "how to flush a manual toilet" that you should give guests anyway unless you want to spend a lot of time clearing clogs are, "make sure the plug is in the sink." The only time you'd flush with fresh water will be just before the boat sits, after you've closed the thru-hull, to rinse all the sea water out of the system....and you're the one who'd be doing that, not your guests.
The average manual toilet flush is about .5 gallons...so a 3 gal tank is good for only about 6 flushes. Since the average adult uses the toilet 5x/24 hrs, you'll spend half your time refilling it....how do you plan to do that? You can't connect it to your fresh water plumbing...so you'll have to install a separate fill...Or you can spend a lot of time using the shower head to refill it...but the tank will have to be vented no matter how you fill it. And you're gonna put a LOT more of your fresh water down the toilet than you need to.
If you believe you really need a separate tank for the head to flush it with fresh water, why not tie the tank into the sink discharge line with a diverter valve. Then you could easily fill the tank by turning the diverter valve and then filling the sink.
Btw...
You DO explain to your guests how to flush a manual marine toilet--the correct use of wet and dry modes and how to add water ahead of solids--and make sure they know what should never EVER go into one?
You DO explain to your guests how to flush a manual marine toilet--the correct use of wet and dry modes and how to add water ahead of solids--and make sure they know what should never EVER go into one?
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