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Old 10-20-2017, 10:23 AM   #1
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Draining a water tank help

Hi All,

I have (2) 75 gal water tanks, somewhere between 1/4 and 1/2 full. I need to drain them (old water). Does anyone know of a sump pump set up that will work?

GOD, Family, career
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Old 10-20-2017, 10:42 AM   #2
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City: North Charleston, SC
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1) Pump the water out with your boat's water pump. Just turn on one or more faucets.

2) Some boat water tanks have a drain. Hook a hose to it and open the valve.

3) Disconnect the water lines from the tanks and let them drain into the bilge.
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Old 10-20-2017, 10:42 AM   #3
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Why not use your domestic water system and just dump it in the sink? If your pump is 3 gallons per minute it won’t take very long. You’ll probably need to clean the screen on the faucet when you’re done though.
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Old 10-20-2017, 10:56 AM   #4
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I drain mine through a freshwater washdown spigot on the bow (foredeck) to avoid draining into a sump box. this way it drains out a scuper. No sense in running 2 pumps (one to drain the tank and one to discharge the water from a sump box).
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Old 10-20-2017, 11:01 AM   #5
City: Carefree, Arizona
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I drain mine to the bilge once per year and flush it out a few times with bleach while doing so. Done it this way on several vessels i've owned over the years.
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Old 10-20-2017, 11:07 AM   #6
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I took off a threaded elbow just downstream of the isolation ball valve and put on a tee with a plug just for this purpose. Drain to the bilge in the winter or long periods of non use.
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Old 10-20-2017, 11:11 AM   #7
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Mr. DE. For the small volume of water involved, the suggestions thus far, depending on the geometry of your tanks, are most probably the best and most cost effective.

We carry 550 gallons (US) and I've invested in a submersible sump pump to drain the tank, when necessary.

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Old 10-20-2017, 12:04 PM   #8
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Be careful with the bleach suggestion as you have stainless tanks. Read up on it before doing it as the two don't mix well.
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Old 10-20-2017, 03:31 PM   #9
City: Carefree, Arizona
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Bleach and SS are quite compatible in the strengths commonly used for water and systems treatment. But, I have heard dock talk to the contrary, old wives tale maybe. Jbear, could you point me towards a book or treatise on this. My commercial water treatment past use using Cl gas used SS equipment liberally.
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Old 10-20-2017, 04:45 PM   #10
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According to the Australian Stainless Steel Association, 304 stainless is ok with up to 2ppm chlorine long term. 316 stainless is good for 5 ppm.
Higher concentrations are ok for short term disinfecting.
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Old 10-20-2017, 08:22 PM   #11
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The real problem is chlorine in aluminum tanks.
Lucky Lucky
Stuart, FL
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Old 10-20-2017, 09:58 PM   #12
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Concur with the drain to bilge folks. Bilge pump is 'way more than adequate. You'd have to wait for a coon's age to pump the water out with the water pressure pump.
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Old 10-20-2017, 11:46 PM   #13
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I bought an old, used, Jabsco diaphram pump that worked.

Set up a soft copper diptube , 3/8 od , which can be slid down the tank filler hose until it hits the tank bottom. The hose on mine is not truly straight so the copper has to be tweaked a bit to get it to go down. Cut the end of the copper on at least a 45o angle. Used some hose to connect the two. Setup an overboard hose from the pump.

I used garden hose couplings, male and female, to connect it all.

Mount the pump on a piece of plywood a bit bigger than the pump. Mine, while running, slid and flipped and put a scar in the gelcoat. Small but annoying.

I then leave the pump to do it's thing. At 3 gpm I can estimate how long I have to do something else. Coffee, read, fool with some thing else. The nice part about these pumps is they can run dry for a long time without being damaged.

I take my boat out with the tank ~ 1/3 to 1/2 full with the pump and diptube setup on a rough day. Get that water slopping around inside the tank with pitch and roll and run the pump and it will clean the tank.
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Old 10-20-2017, 11:47 PM   #14
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Won't draining the tank into the bilge sink the boat? Wait, what? Never mind.
Parks Masterson
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