anyone help re holding tank

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Hi all
I am thinking of fitting a holding tank does any one know the minimum number of tank fittings which would be required, so far I have waste in, waste out to seacock, waste out to deck pumpout, and vent.

Would it be feasible to share the waste out to seacock and waste out to deck pumpout via a diverter valve or do they have to be separate?

cheers for any comments
 
All I have is waste in, with a Y-valve to the seacock, vent and waste out. There were no pump out facilities available in my usual haunts when I fitted it, to avoid antisocial pumpings in confined harbours, so it is pumped out "at sea".
Not sure about sharing the deck pump-out with the sea outlet, I thought the pump out station provided the suck to remove the stuff, rather than the pump on the boat, so you may have to tee off before the pump and fit a shut-off valve. It may be easier to fit a fourth outlet anyway.
 
Is it possible to fit a gravity tank? This will cut down the number of fittings as the original seacock also works as the shut off for the tank and obviates the need for splitter valves etc.. If this is poss and you're considering going down this route let me know and i'll give you what meagre information on the subject I possess.

Chas
 
Is the bottom of the tank above or below the water line? Is the waste out to seacock pumped or gravity?

Assuming it is below the water, then the waste would be pumped out and so combining the two outlets would mean using a diverter valve. Otherwise when the suction hose is placed on the deck fitting it will just pull air from the anti-siphon valve in the seacock outlet. Waste pumps will let air through their valves backwards. Under waterline holding tanks have enough of a problem with pump out facilities due to the height they need to raise the liquid by suction. In Alameda we calculated the pump needed 10' of suction head. Pump was a waist height on a tall pontoon. Any leaks will ruin this. But then this will be a infrequently used diverter valve so see below. Using 2 outlets from the tank would be better.

Putting the pump before the Y (one going to the seacock and the other to the deck fitting) would help. But the chances of switching the pump off and on incorrectly and covering the deck is not practical! Since the deck seal is dependant on a rubber nozzle held in by a human.

If the tank is above the water, and pumped to the seacock, then there is no need for a anti-siphon so there can be no air leaks. All seacock pipes have to be reinforced for vacuum operation as well as pressure. One outlet would do.

If the tank is above the water, and gravity to the seacock, then the fitting is in the base of the tank and a single outlet is OK. Just a Y is needed to the deck plate.

If you can avoid it, do not use unnecessary diverter valves. If possible use 2 straight ball valves than one diverter type. Most diverter valves use a D shaped baffle that rotates in a cylinder to close of the unused port. This means that the sliding surface that the D must move around is exposed to deposits and the valve will jam. Ball valves only expose the bare minimum of the ball to the closed off pipe. Any deposits on a ball are forced away from the ball into the liquid but a Diverter valve compresses the debris outwards on to the wall of the valve. We have tried and abandoned the small back ones (plastic handle), the grey type with metal handles, and the huge rotating port type.

Different sea waters around the world have different deposition rates so nothing should be judged by home port experiences.

In our boat we like to remove the tanks regularly (2 years) but this normally means pulling the 2" hoses off the tank outlets. This destroys the hose ends and causes problems. We now fit a 2" to 2" adapter in the end of the expensive hose so that a short length (4") of sacrificial hose then connects to the tank. Removing the tank then is just a case of cutting the sacrificial hose. Takes a little more room but it has saved a lot of fighting in small compartments with large hoses.
 
[ QUOTE ]
Hi all
I am thinking of fitting a holding tank does any one know the minimum number of tank fittings which would be required, so far I have waste in, waste out to seacock, waste out to deck pumpout, and vent.

Would it be feasible to share the waste out to seacock and waste out to deck pumpout via a diverter valve or do they have to be separate?

[/ QUOTE ]

Here's how I'd do it:

Line from toilet to fitting at or on the top of the tank, with a y-valve inline...one side to the tank, the other to a thru-hull so you can flush directly overboard at sea instead of going into the tank.

Vent (I recommend 1" instead of the usual 5/8") on the top of the tank, positioned toward the centerline away from the hull, vent line to a thru-hull high enough on the hull to keep it out of the water at maximum heel.

Tank discharge--either at the bottom of the tank, or preferably on the top of the tank with a tube inside to the bottom--is typically just one line with a y-valve...one side to the deck pumpout fitting, the other side to a pump and thru-hull. However, I recommend going with TWO discharge fittings instead...one directly to the deck pumpout fitting, the other directly to the pump and thru-hull. This eliminates the need for a y-valve in the discharge line.

Tek-Tanks has an excellent article (at least I think so, since I wrote it <g>) on how to install and maintain a tank on their site at http://www.tek-tanks.com/sanitation/sanitation_index.html

And I'm always glad to answer specific questions.
 
You should fit the all discharge pipes to the top of the tank, with internal tubes. Then in the event of a leak the contents do not end up in the bilges.
 
Listen to the Headmistress. Wot she doesn't know about the subject ain't worth the learning.

My installation is exactly as she describes. No pongs at all!!!! /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
 
My tank has just a single output fitting going via a pump to the through-hull. I plan to add a deck pump-out. Circumstances mean that adding a second output to the tank would be difficult.

Do I need a valve on the Y-piece for the new output or can I get away with a simple Y?

Alan.
 
You CAN use a tee...but I would go with a y-valve, and put it close to the tank...so you can shut off the flow of waste to the pump to service it. 'Cuz nobody ever discovers that the pump or macerator isn't pumping when a tank is empty, only when it's full.
 
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