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Old 28-09-2018, 06:29   #1
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Holding Tank not draining

Houston, we have a problem!

Yep our aft holding tank will not drain and is 90% full. **** most definitely happens

What I need are options on how to get it to drain without putting excrement everywhere and without any specialist kit or tools. I have checked at is isn't an air lock or blocked air vent issue as I undid the access nut on the top but nothing happened. I think it is the bottom of the tank where the drain hose attaches as a small amount of "brown" did drain from the seacock when I first opened it (at sea 3 miles off before anyone howls).

One option is to use a thick bit of spare cable attached to a thin line through the access nut to try to break up whatever crud is lying at the bottom of the tank. A second is to feed a stiff but flexible wire up through the thru-hull along the drain hose and into the bottom of the tank - not an easy option as there is a 90 bend and of course the thru-hull is underwater.

If we can't pump out which is looking highly unlikely as there are no facilities where we are currently then we have got to do something to clear the blockage and clean the inside of the tank. I'm thinking chemical warfare with something like Mr Muscle Foaming Pipe Unblocker or similar. Any ideas on if this would work?

Ideas, the simpler the better, gratefully received

Cheers

Keiron
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Old 28-09-2018, 08:52   #2
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Re: Holding Tank not draining

From your description, I'm guessing that your tank is entirely above the waterline and so it gravity drains through a fitting IN the bottom of the tank. If so, you've just learned the hard way that sludge can build up in the discharge line and pack it solidly if the thru-hull isn't opened fairly frequently to get rid of it and rinse out that line.

There are a couple of products sold here in the US that might work, but have no idea whether they're available in the UK...and they'd take quite a while diluted in full tank if they did work. So about all I can offer is an off-the-wall suggestion--IF it's even possible (I don't think you have any choice but to ignore legality in this circumstance):

If you can dive on the thru-hull with a stick in your hand (broom handles are typically 1" diameter, which should be small enough to stick into the thru-hull), have someone else inside the boat at the ready to open the seacock so you can jab in it into the hose. May require several pokes. Once it's clear, put a few gallons of water into the tank via the deck pumpout fitting--'cuz that sends the water into the tank at the bottom to stir up any remaining sludge and hold it in suspension so it will drain out of the tank.

As I said, that's definitely "off the wall" but I can't think of any other way to clear the drain line from outside of the tank.

And in the future, regularly rinse out the tank using the method I describe to prevent this happening again.

--Peggie
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Old 28-09-2018, 09:01   #3
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Re: Holding Tank not draining

Had some success with using our deckwash hose extended with a garden hose to force water back up from the hull fitting using the dinghy to get to the fitting. Be prepared for the resulting deluge if you are successful Best of luck....
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Old 28-09-2018, 09:03   #4
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Re: Holding Tank not draining

Perhaps a drain snake or auger from the outside through the seacock. They can make it around surprising bends.

Or with phenomenal luck from the pumpout fitting if the entry and exit are in line. Unlikely though.

OR
a manual pumpout setup. I've never tried it but a pumpout fitting and a hand or electric diaphragm waste pump may help.

Best of luck.
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Old 28-09-2018, 09:17   #5
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Re: Holding Tank not draining

Hi all and thanks for the various ideas

Managed to pick up some chemical to attack the mess so giving that a try. Fingers crossed in 24hrs we have a gurgle.

Peggie - yes you are correct it is gravity drained but both our holding tanks are regularly drained and fully flushed through at the end of each trip out to the boat. Have drained some nasty sludge from the forward heads in the past so know exactly what you mean, hence why we have been pretty fastidious about flushing them regularly. Unfortunately due to the 90 bend at the seacock there's no way a 1" diameter pole is going up there.

Dfelsent - yep you are correct the pump out exit and entry are not in line, what a surprise as nothing is never that easy on a boat is it. In fact on this tank the pump out hose comes down the side, traverses the base of the tank and connects next door to the drain pipe. Only hope of trying to dislodge anything would be undoing the access port on the top and trying to wiggle something around in the tank.

Takamoana - had a poo fountain once already when the vent line blocked and the tank looked like stomach after a massive meal. That was not nice and an experience I do not want to have to repeat.

Oh and the product I have got also works for regular degunking so there's another job to add to the end of season "**** list"
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Old 28-09-2018, 09:22   #6
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Re: Holding Tank not draining

I like gravity feed systems. I find it especially helpful to have the inspection port located directly above the discharge, making it easy to snake from above. I think 90 degree bends and horizontal runs on the discharge hose are asking for trouble.

If you can't snake it from above, you may have to from in the water, but as you said, be prepared to swim away fast when it works! Hopefully someone inside can close the valve for you the second it starts draining properly.
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Old 28-09-2018, 11:45   #7
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Re: Holding Tank not draining

Nautical62 - totally agree with you that 90 bends in plumbing systems and horizontal sections are a nightmare for drainage. We have a horizontal section in our drain from the sink at home and it is a right PITA but like on the boat there's nothing that can be done about it, the space limitations are what they are.

Just wish I had a proper inspection port in the tanks. All I have is a small, screwed on stopper in one corner that allows me to vent the tank should the vent port get blocked for whatever reason. Certainly not big enough to get more than a 10mm diameter probe into if I could bend it round to get it in through the cupboard.

Begs the question why don't designers think about these things when they create these spaces? I think it would be lovely to get the muppet who designed these holding tank cupboards on my boat on board and get them to figure out how to fix the problem.
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Old 28-09-2018, 11:58   #8
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Re: Holding Tank not draining

Unfortunately due to the 90 bend at the seacock there's no way a 1" diameter pole is going up there.

I had 2nd thoughts about the broom handle after I posted...and wished I suggested a long bladed screwdriver instead...'cuz whether it's packed with sludge or--since you say you do rinse that line out regularly--sea water mineral buildup, you'll do better with a tool that can break it up. I suspect the worst impaction will be at the thru-hull, so it may not take too much chipping to open it up enough to start tank contents flowing, if only a trickle. Muriatic (hydrochloric) acid is the best thing to dissolve mineral buildup in hoses.



--Peggie
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Old 28-09-2018, 21:30   #9
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Re: Holding Tank not draining

I had a similar problem and a old style plunger used on the seacock worked well. Like someone else said, be prepared to quickly swim away

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Old 29-09-2018, 09:37   #10
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Re: Holding Tank not draining

I've heard someone using an air-horn (the handheld type with a compressed air bottle), holding it to the seacock. The pressure from the air, and the vibrations might work wonders.
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Old 29-09-2018, 09:41   #11
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Re: Holding Tank not draining

We had a similar issue a while back. Our F/G tank had no inspection port...so I (very carefully as the tank was near full) cut the hole and added one! I also replaced the original 3/8" vent hose with a 1" vent hose-and discovered the old one was clogged in several places, as well as at the tank and at the vent port. Then I added a "waffle pump"(vs a macerator pump) as a pump-out device, and successfully drained the tank. We've had no issues since.
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Old 29-09-2018, 10:59   #12
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Re: Holding Tank not draining

It sounds as if you are depending on gravity. You really need to install a macerator pump.
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Old 29-09-2018, 11:00   #13
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Re: Holding Tank not draining

Ours blocks regularly and the same on our last boat. For us the problem happens if we try to empty it when its not full enough so there is not enough weight to make enough pressure.
I have 3 wire coat hangers opened up and joined together making a 3m bit of stiff wire which I jam in from the top pump out fitting and find the hole in the bottom of the tank. Its a mission to find the hole with a lot of probing needed and then force the wire right down to the through hull fitting but i have done it at least 10 times over the last 1.5 years and 15,000nm of sailing. Its doable and not too messy. Good luck.
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Old 29-09-2018, 13:11   #14
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Re: Holding Tank not draining

My holding tank had its own pump for pumping it out, through a siphon breaker.me siphon breaker that the normal discharge-to-ocean plumbing uses.

If you do not have this system, you are going to have to pump it out via the deck pump-out using a portable pump, or install a sludge pump and siphon breaker before the sea-cock which itself could be the problem. Marine life like to build stuff in the through hulls that seldom have anything coming through them.
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Old 29-09-2018, 14:49   #15
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Re: Holding Tank not draining

My stainless tank plugged too. The vent line was plugged solid, so I replaced it. Then it still wouldn't pump. I figured that old sediment reached up into the suction tube extension. Phosphoric acid and a short trip offshore did the trick.
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