I apologise if this is answered somewhere else, but I can't find the answer.

I have an above-ground pool, with an overflow pipe coming out of it about 4" from the top. This overflow pipe then goes down under the ground, under my garage and comes back up under the house where it has to rise enough to get into a drainage pit. The height it has to rise to is about 12" below the height at which the pipe exits the pool.

But the water won't rise that high! In fact, it will only rise to about 2 feet lower than it needs to. I don't understand this. Shouldn't the water rise to the same level as the pipe exits the pool? The size of the pipe that goes down from the pool is much smaller than the size of the pipe that comes up from the ground inside the house. Could this be the reason?

Can anyone point me to somewhere that explains this? I'm totally stumped - it feels like the laws of physics are breaking. Could it be that just installing a smaller pipe will allow the water to rise higher?

thanks for any help

Here's a diagram (maybe, need OP to confirm it matches what they intended). The red line would be the pipe and the blue line inside the red pipe denotes the water level. enter image description here

  • Are you in Australia? Does your toilet flush in the other direction? – DMoore Feb 2 at 5:18
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    Diagram and pictures would be very helpful. – whatsisname Feb 2 at 5:59
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    In the middle of the pipe run there is an additional pair of up and down U bends, partially filled with air. – Polypipe Wrangler Feb 2 at 9:29
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    Force water through pipe, then check again. – Polypipe Wrangler Feb 2 at 9:36
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    Classic trapped air behavior. If you force water through to remove the bubble(s) it should start flowing again. Siphons can be very picky. – Ecnerwal Feb 2 at 14:07

It is sort of a siphon and you have a problem common to siphons , air lock. Air pockets interrupt water flow. You can pump water into the pipe to push out the air but unless you have a constant flow of water ,air will get in again. The U bends you refer to in comments are likely the main problem. With no air ,the water levels at each end of the pipe will be exactly the same.

  • Thank you. I don't have u-bends, but I'll work on trying to get rid of air in the line. – Dean Feb 4 at 4:28

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