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Old 10-01-2012, 22:46   #1
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Gravity Holding Tank Won't Drain

I'm looking at revising my head/holding tank arrangement, and would appreciate any/all advice. Please note that I live in Canada where pumping overboard is allowed in open water.

The Jabsco manual head on my sailboat pumps into the top of a holding tank; the holding tank drain goes to a 'Y' valve, which directs it to either a deck pump-out, or out of the boat via the through-hull. The tank is well above the water line, so when I replaced the hoses etc. I confirmed it could drain well by simply having the Y-valve in the right position and opening the through-hull. However, in practical use - as in our recent summer vacation - it would not drain, but became plugged as the solids in the tank had collected on the bottom, at least partially blocking the drain. All waste hoses are standard 1.5" and new. I was able to do the unclogging but will not dwell on the details here - just let it be said that I am keen on avoiding this scenario again.

I'm considering one of the following options:

1) Installing an macerating head - if the waste was macerated before it got into the tank there should be much less chance of blockage; the downside is I'll have to wire in a circuit for it and have more things to drain my batteries and possibly breakdown. Space is also an issue, as most of the electric heads I've seen are larger than my current Jabsco Twist-Lock, and I'm not sure that they'd fit.

2) Installing a manual or electric pump to drain the tank - pulling the waste out, instead of just relying on gravity, would hopefully allow the tank to be emptied reliably. Downside here is that the pump would have to be at least 2-3 feet downstream of the tank, and I'm not sure if additional suction would empty the tank, or just make the clog worse by pulling more stuff into the hose. Space is an issue here too, since the only place to mount the pump would be under the sink and that space is already full of plumbing.

Any advice on which of the options would be a better choice? Are there any other alternatives I should be considering? Thanks!
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Old 10-01-2012, 22:52   #2
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Re: Gravity holding tank won't drain

Ben;

How long did you let the contents sit in the holding tank (ballpark) before you tried to empty it out? How big is the holding tank?
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Old 10-01-2012, 22:59   #3
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Re: Gravity holding tank won't drain

I've been in your shoes one too many times... and I know the unpleasantness that is required to get the tank empty....

I think you have two issues to deal with. First and foremost you need a pump on your tank... the gravity drain idea just doesnt work with solids... even macerated solids / paper will gel up and not flow well. Best bet is a large diaphragm pump.... easy and simple. An electric will probably give you more issues that you dont want.

Second, a macerating toilet will definitely make what ever you are pumping flow better... The Raritan Sea Era may fit and gets great reviews... Stay away from the Jabsco electric unit as is cant really handle much going throught to start.
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Old 11-01-2012, 00:05   #4
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Re: Gravity holding tank won't drain

I guess that diminishes the theory that siht rolls down hill.


Sorry! Couldn't resist.

BTW welcome aboard Ben!
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Old 11-01-2012, 05:42   #5
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Re: Gravity holding tank won't drain

Greetings and welcome aboard the CF, Ben.
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Old 11-01-2012, 05:52   #6
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Re: Gravity holding tank won't drain

Quote:
Originally Posted by Ben 331 View Post
I'm looking at revising my head/holding tank arrangement, and would appreciate any/all advice. Please note that I live in Canada where pumping overboard is allowed in open water.

The Jabsco manual head on my sailboat pumps into the top of a holding tank; the holding tank drain goes to a 'Y' valve, which directs it to either a deck pump-out, or out of the boat via the through-hull. The tank is well above the water line, so when I replaced the hoses etc. I confirmed it could drain well by simply having the Y-valve in the right position and opening the through-hull. However, in practical use - as in our recent summer vacation - it would not drain, but became plugged as the solids in the tank had collected on the bottom, at least partially blocking the drain. All waste hoses are standard 1.5" and new. I was able to do the unclogging but will not dwell on the details here - just let it be said that I am keen on avoiding this scenario again.
We have the same problem and I guess we need a pump but a temporary solution has been to top the tank up with sea water and open the seacock when we have a bit of speed up, the head of water in the tank coupled with the flow past the seacock seems to help pull the contents from the tank.
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Old 11-01-2012, 05:52   #7
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Re: Gravity holding tank won't drain

How about a composting toilet. Go all season before dumping the compost
Nature's Head Composting Toilets - The environmentally sustainable waterless toilet for Your Boat, RV, Cabin, Big Rig, Barn, Workshop, or Yurt!
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Old 11-01-2012, 06:29   #8
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Re: Gravity holding tank won't drain

Add a macerator. But when the shyte turns semi-solid after the tank rolls over turning to wet concrete, all bets are off.
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Old 11-01-2012, 10:35   #9
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Re: Gravity holding tank won't drain

Welcome aboard, Ben. We installed a macerater pump between the tank and the output through-hull, and I think it's the best bet. But install it where it's easy to get to, because something will someday clog the macerator.
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Old 11-01-2012, 10:47   #10
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Re: Gravity holding tank won't drain

I had similar problem on a Nauticat 37 which has no Y valve; there is no way to bypass the holding tank. Scale had built up in the holding tank and a vigorous sail managed to shake it off and plug the outlet.


We went to the pump out station at Port Hardy and emptied the tank. We tried plugging the vent and attempting to the dislodge the blockage by using the suction of the pump - no luck.

We then filled the tank with fresh water and emptied it about 5-6 times. After disconnecting the discharge hose from the thru-hull, we ran a snake up the hose and managed to dislodge the scale.
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Old 11-01-2012, 10:52   #11
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Re: Gravity holding tank won't drain

snaking a clogged sewage hose upside down sounds like a job i would avoid at all costs i too would want some kind of pump not relying on gravity to get the work done.
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Old 11-01-2012, 11:14   #12
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Re: Gravity holding tank won't drain

My gravity tanks have 60mm hose on the outlets (with comparable size valve). They've never plugged (yet).

The original hose was wire wound, and the wire rusted as the rubber got permeated. I had to go back to Europe to get replacement hose, I couldn't find sanitation hose that size (or even close) in the US. The new hose does not have wire in it, so hopefully it'll last longer.

I wondered how well the 1.5" stuff works, obviously not real well on the outlet of a gravity system.
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Old 11-01-2012, 11:16   #13
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Re: Gravity holding tank won't drain

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snaking a clogged sewage hose upside down sounds like a job i would avoid at all costs i too would want some kind of pump not relying on gravity to get the work done.
A pump / macerator would not have helped. Any holding tank may develop scale.
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Old 11-01-2012, 11:30   #14
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Re: Gravity holding tank won't drain

It's a real dilemma. I have had two gravity tanks with no issues, both were small (8 gal) and both drained very well. Yet "where there's smoke there's fire" surely applies and others on this board have had problems... guess I was lucky! Do you use a lot of paper?
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Old 11-01-2012, 11:43   #15
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Re: Gravity holding tank won't drain

The problem: Sludge is collecting/building up in the discharge line...you're not putting nearly enough water into the tank to turn that sludge into a slurry that's less likely to create a clog. Macerating the waste before it goes into the tank won't help...maceration just creates sludge as it comes out of the toilet instead of letting it occur in the tank as waste dissolves in it...so you'll still get a buildup of sludge in the line.
The routing of the discharge hose can have a lot to do with it. Is the discharge port IN the bottom of the tank? Or on a side/end of the tank AT the bottom? If it's not plumbed so that waste will flow through the tank and out the thru-hull any time the seacock is open, that's a major cause of your problem.

If the discharge port IS in the bottom of the tank, if the discharge line is not a straight downhill shot to the thru-hull, THAT'S a major cause of your problem...'cuz sludge will build up first where there's any horizontal run.



Leaving us with two possible solutions:

1. Put a LOT more water in the tank with each flush...add water before dumping. Dump it a LOT more often. Rinse out the tank every time you pump or dump it...or...

2. Correct the plumbing or install a pump to dump the tank.
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