Holding Tank Discharge Plumbing

[Drift Woods]

Do yourself a favor and use a T and shut the seacock. I changed out two frozen Y valves on my last boat before I wised up. Charging those Y valves is a nasty job.

[peghall]

You should know better than to make a statement like this. Typically the spin-welded fittings are right at the bottom.

If you look carefully at the spinwelded fittings on decent quality tanks, you'll see that the diameter of the melted PE around them is 1.5-2 x the diameter of the actual fitting. Spin welding melts the edges of the hole while simultaneously blending new melted material with it...it needs that much room around the fitting for strength. So a 1.5" threaded fitting would call for about 2.25" hole in the tank. The hole has be far enough above the bottom of the tank to be completely clear of the bottom...so that would put the bottom edge of the inner diameter of the actual fitting an inch or more above the bottom.

And the tank is installed so that it pitches down to this fitting...
Not always, though it's a good idea.

...which allows much more complete evacuation than any standpipe.

No...it doesn't. But, as I've already said...whatever floats YOUR boat is fine with me.

[rwidman]

Originally Posted by Drift Woods

Do yourself a favor and use a T and shut the seacock. I changed out two frozen Y valves on my last boat before I wised up. Charging those Y valves is a nasty job.

If you can find it, a "Y" fitting is better for sewage than a "T". There's less likelihood of a clog.


Peggie's suggestion of standpipes is valid if you are buying a new tank or having one made. It's not worth tearing out an otherwise good tank though. There might be a clearance issue with top mounted outlets. Check before you buy.

[Sailmonkey]

Originally Posted by Cadence

I must be dumb? A diaphragm pump for discharge of a holding tank. I would think a macerator pump makes more sense?

Diaphragm pumps are the gold standard for moving waste. Those spinning blade impeller pumps that have been sold as the cats ass are horrible!!


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[Cadence]

Originally Posted by Sailmonkey

Diaphragm pumps are the gold standard for moving waste. Those spinning blade impeller pumps that have been sold as the cats ass are horrible!!


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I believe a true macerator is more like its name not an impeller pump?

[thinwater]

Originally Posted by peghall

I disagree...two separate discharge lines is a lot simpler that one with a y-valve that may be used so seldom that it freezes...or the handle breaks.

I just replace a valve due to broken handle. Easy, but pointless $$$. I probably hadn't moved it but once every 3 years, and you can't very well "exercise" the valve if it must be kept locked.

As for a T-fitting, I've got a good idea that pipe and likely the pump will get rammed full of solids. More fixing.

So yes, separate pipes sounds smarter and probably cheaper.

[Cruisingscotts]

Ickk...............

Advice to take or leave...

If you are starting from scratch.

Simpler is much better..

1ea. Gravity drain holding tank, false bulkhead use a locker etc. Min 50gal if possible.

1ea. fitting on bottom of tank side etc with isolation valve conecting to tank. Where ever possible use plastic fittings and valves.

1ea. top fitting with down pipe for deck suction.

Use Schedule 80 PVC pipe and rubber boot connections for all plumbing runs if possible. PVC true unions to remove pipe sections or equipment are invaluable

White sanitary hose will need to be changed every couple years period.

You will need to accept that you are going to be in 1 of 3 schools no exceptions

A. Maintain a chemical and acid treated sewage plant, regular pump outs and or Type 1 Electro scan with weekly dosing of acid to remove unrine related build up

B. Maintain biologically treated sewage plant with regularl pump outs and or approved treatment plant let enzymes take care of nasties.

C. Ignore the above two and spend lots of time working with poop

[Sailmonkey]

Originally Posted by Cadence

I believe a true macerator is more like its name not an impeller pump?

The macerator pump you buy from the boat store is an impeller pump. It just so happens to have a knife inside also.

http://www.go2marine.com/docs/2/1/0/1/210183F-p.jpg


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[sy_gilana]

Our Holding Tank is fed from a Raritan Crown Head, via a Y valve that can select Direct Overboard, or to tank.

The tank's inlet goes in the side, and internally reaches across to the other side to prevent heeling backflow.

The tank's outlet/suction goes to Jabsco Diaphragm pump, then through a loop near deck and back down through a ball valve seacock just above waterline. At the top of the loop is a siphon break, and a tapering tube that goes to the deck plug.

To pump overboard, we switch on the pump, and leave the seacock open.
To pump into a drum ashore, or a tanker, we shut the seacock and switch on the pump after opening the deck plug and connecting the hoses.

[ranger58sb]

Originally Posted by wayne.b

My question is whether or not I need a Y-valve to redirect the output, or if a simple T-fitting will suffice. I'd like to go with a T-fitting for simplicity but I'm not sure if the check valves in the pump will be sufficient to prevent back flow when pumping from the deck. Another alternative would be to close the sea cock when pumping from the deck but that requires remembering to open it when pumping overboard.

Our builder-installed system uses a single T near the bottom of the holding tank. One line from the T goes to the deck discharge for pump-outs, and the other leads to a macerator pump... which in turn leads (over a big loop) to a seacock on an underwater thru-hull.

The seacock must be closed when the macerator is not in use, else the holding tank will backfill with seawater.

-Chris

[CaptTom]

Here's what I did: PVC 90-degree elbow at the bottom (outlet) of the tank, with another length of PVC up to a tee just above the level of the top of the tank.

The macerator sits on top of the tank (on a square of marine plywood.)

The "base" of the tee goes to the macerator input, via sanitary hose. The other "arm" of the tee now faces up, with a sanitary hose to the deck pumpout.

The benefit of this arrangement is there's nothing that should ever need replacing below the "water level" of the tank, only hard PVC. There are, however, hoses between everything to absorb vibration.

You do run the risk of sucking seawater up from the thru-hull, through the macerator, and to the tee. Depending on your how much resistance your macerator adds, and the length of the run, you may or may not get the waste out before that happens. Obviously, being able to close the thru-hull easily would negate that.

[peghall]

Our builder-installed system uses a single T near the bottom of the holding tank. One line from the T goes to the deck discharge for pump-outs, and the other leads to a macerator pump.

Builders like to use tees because they're cheaper than y-valves. The main disadvantage to a tee is, coming out of the tank at the bottom there's no way to shut off the flow of tank contents if you have to work on the macerator...and you NEVER discover that a macerator pump isn't working when the tank is empty. If you don't want a y-valve, you can solve that problem by installing a shutoff valve on the tank discharge fitting.

[ranger58sb]

Originally Posted by peghall

The main disadvantage to a tee is, coming out of the tank at the bottom there's no way to shut off the flow of tank contents if you have to work on the macerator...

Correct. And our macerator is currently not working... for the last few years... partly because changing it can be an issue (but also partly because I'm considering a Purasan replacement).

OTOH, a Y-valve at the tank instead of a T could still mean a full hose full of... well, you know... in between Y and macerator...

-Chris

[senormechanico]

The more I read, the more I like my ElectroScan.

[Cadence]

Originally Posted by Sailmonkey

The macerator pump you buy from the boat store is an impeller pump. It just so happens to have a knife inside also.

http://www.go2marine.com/docs/2/1/0/1/210183F-p.jpg


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I guess we should buy a sink food disposal. It is only used food.