Holding tank discharge via thru-deck opening

[rwidman]

This is what I suggested above. Here it's pumping into a sewer but it could just as easily pump into a container or even overboard.

[twinboat]

I was showing the picture of them pump as an example of putting slight positive pressure on tanks.

If you read any of this post, you would have seen that I suggested using the pressure from the head to pressurize the holding tank.

This light pressure would only be until the effluent reached the height of the elbow on the pump out port and started down the hose, to a point where the siphon would start.

Once a siphon started, the pressure would be removed and the vents would have to be opened to let air flow in and replace the siphoning effulent.

It would be as simple as flushing my Vacuflush head, with the water supply off, after attaching the hose and holding a gloved finger over the tank vent, until the flow started.

[senormechanico]

Originally Posted by twinboat

I suppose that could happen.

I do have a Vacuflush system so whatever makes it to the tank is mashed up thru the bowl and then the piston pump first.

If I try this, I will check the clamps on the discharge hose.

All of my tank fittings go in the top of the tank. At least it won't drain out if a hose comes off.

Be sure and take a video when you do.

Post it on Youtube and if your system blows apart you'll get millions of views !!

[peghall]

Give it a try and let us know how it works!

[sanibel sailor]

COUSIN EDDIE !!!!!

[peghall]

In the late '70s or early '80s,just as holding tanks began to be required, Jabsco came up with a combination pumpout/discharge deckplate that had two holes in it--a 1.5" pumpout connection and a 1" hole for overboard discharge...the idea being, the macerator would shoot the tank contents out that hole. I've actually run across two boats on which they'd been installed..a sailboat with it in the side deck and a Grand Banks trawler with it in the side of the hull...neither still in use, neither owner could figure out what it was. I found out from someone who'd worked at Jabsco when they came up with this idea. He told me, "One of the reasons the impeller discharge pumps have a 1-1/2" threaded end is because the original thought was that you could screw that in to discharge though the deck plate, but it was never adopted because of the mess issue. There were a number of blow up disasters trying to pump through the deck discharge plate." He confessed that a couple of tests when that side of the boat was to windward weren't too successful either!

[sailorchic34]

You really really don't want to pressurize a holding tank. Physic's is a bitch.

First a holding tank and really the entire sanitary system is not designed for pressure, at all. To lift a liquid up 6 feet in a 1-1/2" hose will take about 4.5 psig. psig= pounds per square inch gauge. Hardly anything right. Hold that thought.

Lets say you have a 20"x20"X20: holding tank. At 4.5 psig, one wall would have a force of 1800 pounds trying to push it out. Same for the other 5 sides too. If your holding tank has a longer side, say 30 inches, then that side would have a force of 2700 pounds against it. Something will give and when it does, it will not be pretty.

To quote, Spengler from Ghostbusters, "It would be bad".

Don't go there.

If you try it, please put the seat down first. You'll be slightly happier for that.

[twinboat]

Originally Posted by sailorchic34

You really really don't want to pressurize a holding tank. Physic's is a bitch.

First a holding tank and really the entire sanitary system is not designed for pressure, at all. To lift a liquid up 6 feet in a 1-1/2" hose will take about 4.5 psig. psig= pounds per square inch gauge. Hardly anything right. Hold that thought.

Lets say you have a 20"x20"X20: holding tank. At 4.5 psig, one wall would have a force of 1800 pounds trying to push it out. Same for the other 5 sides too. If your holding tank has a longer side, say 30 inches, then that side would have a force of 2700 pounds against it. Something will give and when it does, it will not be pretty.

To quote, Spengler from Ghostbusters, "It would be bad".

Don't go there.

If you try it, please put the seat down first. You'll be slightly happier for that.

At last, someone with some convincing data as to why it may not work.

I was never satisfied with " You just can't do that".

The top of my tank is about 20 inchs below where the elbow in the discharge fitting would be. If I was in international waters and had a full waist tank and no pump out avalable, I may try it.

Thanks, it was an interesting debate.

[ontherocks83]

Originally Posted by reed1v

Be on the lookout for periscopes however. My naked wife found that out to her embarrassment.

I hope that is a true story because that is precious! Did she wave and laugh along or get weirded out? I personally would have stripped naked next to her and started doing the truffle shuffle at the periscope just as a goof.

[Siberianhusky]

Made my own pump out last year using a manual bilge pump a plumbing elbow and some pipe. The elbow is 1 1/4, threads right into the deck plate, same thread, homedepot plumbing section provided all the new parts.
Pumps into a 45 gallon plastic barrel which then gets pumped into a septic tank.
Works on vacuum, slick setup cost me about 20$ in new parts.
Saves me a trip through the Murray Canal everytime I need to empty the tank, was a near full day excursion.
I mix a bucket of bleach and water for cleanup whenever I pump out anyway, pump some through the bilge pump and hose - clean enough.
Could easily use the same rig to pump out offshore, just no barrel attached to the discharge hose.

http://www.tank-depot.com/product.aspx?id=755
Homemade version of this

[David B]

[QUOTE=Pizzazz;2035481]I am thinking of removing the thru-hull discharge of my holding tank and pumping out my holding tank only thru-deck.

On my Hunter 31 the waste from the toilet goes directly to the holding tank. The holding tank discharge hose goes to a Y-valve, one end goes to the thru-deck pumpout port, the other goes through a Whale pump, a siphon, and then to the thru-hull valve.

QUOTE]

Is your holding tank below water level? If not, this is a complicated way of doing it. Much simpler to have the macerator pump (or manual pump) at the base of the toilet, pump up to the top of the tank. Then to discharge, the tank is either evacuated through the normal deck fitting / shore pump-out, or a simple ball valve at the through-hull is opened and the tank empties via gravity. No 'Y' valves, and only the single through-hull ball valve. The other plus, is that with the rush of liquid out of the tank when emptying via gravity (when well off-shore of course), any sludge at the bottom of the tank is swept out also, meaning the tank is much cleaner - especially if you give it a good flush regularly.

As to your suggestion, I share the other contributors views - messy, not sanitary, and time-consuming.

I hope that helps.

[sanibel sailor]

most tanks have the egress at the top, not bottom, just like a fuel tank, for the same reasons. Gravity would require a bottom drain

[David B]

Yes - a large outlet at the bottom of the tank for gravity discharge. Works very well.

[Terra Nova]

Originally Posted by sanibel sailor

most tanks have the egress at the top, not bottom...

No, most have the outlet at the bottom, not the top.

[peghall]

...Much simpler to have the macerator pump (or manual pump) at the base of the toilet, pump up to the top of the tank....

Adding a macerator or manual pump to a toilet discharge does anything BUT simplify the system...starting with, it becomes a blockage in the toilet discharge line if it isn't operating simultaneously with the toilet's pump. If your toilet--manual OR electric--can't lift bowl contents up to 4", rebuild or replace the toilet...they're all rated to lift at least that high.