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Old 30-09-2022, 16:58   #1
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Gravity drain holding tank: prevent gunk build-up in drain hose?

Our new boat has gravity drain holding tanks already plumbed. We're not going to be offshore for a good 18-24 months, and I'm worried when I pump-out that I won't get the sludge from the hose from the tank to thru-hull pumped out. It's a good 10' for each tank. Worst case is they clog and when we do get offshore, the tanks won't drain.

I think the easiest solution is to add a ball valve immediately after the tank on the drain hose. I can close this and prevent sludge from building up on the rest of the hose. Bonus is that I could remove the handle on this valve and still be able to exercise the thru-hulls.

Am I just paranoid here, or is this a good idea?

TIA
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Old 30-09-2022, 17:37   #2
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Re: Gravity drain holding tank: prevent gunk build-up in drain hose?

Quote:
Originally Posted by shimari View Post
Our new boat has gravity drain holding tanks already plumbed. We're not going to be offshore for a good 18-24 months, and I'm worried when I pump-out that I won't get the sludge from the hose from the tank to thru-hull pumped out. It's a good 10' for each tank. Worst case is they clog and when we do get offshore, the tanks won't drain.

I think the easiest solution is to add a ball valve immediately after the tank on the drain hose. I can close this and prevent sludge from building up on the rest of the hose. Bonus is that I could remove the handle on this valve and still be able to exercise the thru-hulls.

Am I just paranoid here, or is this a good idea?

TIA
Hi, in my opinion the concept is eminently sensible and how I would have done it originally.
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Old 30-09-2022, 17:40   #3
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Re: Gravity drain holding tank: prevent gunk build-up in drain hose?

I put a PVC ball valve on the gravity drain tank I just installed for exactly that reason. ( I also had put one on our previous boat when I installed that holding tank.) I've got a 1-1/2" PVC Tee screwed onto the tank outlet with vertical PVC to above tank level then short 4" section of hose to the deck pumpout, ball valve screwed to the bottom of the Tee, then hose to the seacock, my goal being to minimize sewage sitting in hoses.
Note that it won't empty the hose if it can't pull air in behind the "slug" of fluid (which it does when the tank is empty and air can go down the "drain"), and even any hose above static waterline level will still have fluid in it. Fortunately mine is only a couple feet to the seacock. If something does plug, I can shove a garden house down the deck fitting, straight down through the tee all the way to the seacock.... of course, a different garden hose than I'd use for filling my watertanks!
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Old 30-09-2022, 17:49   #4
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Re: Gravity drain holding tank: prevent gunk build-up in drain hose?

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Originally Posted by Bellinghamster View Post
I put a PVC ball valve on the gravity drain tank I just installed for exactly that reason. ( I also had put one on our previous boat when I installed that holding tank.) I've got a 1-1/2" PVC Tee screwed onto the tank outlet with vertical PVC to above tank level then short 4" section of hose to the deck pumpout, ball valve screwed to the bottom of the Tee, then hose to the seacock, my goal being to minimize sewage sitting in hoses.
Note that it won't empty the hose if it can't pull air in behind the "slug" of fluid (which it does when the tank is empty and air can go down the "drain"), and even any hose above static waterline level will still have fluid in it. Fortunately mine is only a couple feet to the seacock. If something does plug, I can shove a garden house down the deck fitting, straight down through the tee all the way to the seacock.... of course, a different garden hose than I'd use for filling my watertanks!

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Old 30-09-2022, 18:11   #5
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Re: Gravity drain holding tank: prevent gunk build-up in drain hose?

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Originally Posted by Bellinghamster View Post
...
If something does plug, I can shove a garden house down the deck fitting, straight down through the tee all the way to the seacock.... of course, a different garden hose than I'd use for filling my watertanks!
Well played! I nearly snorted my favorite beverage while reading!
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