A mystery! Spa draining question.


New member
Nov 29, 2020
Yuma, AZ
Hello all,

Thanks to all the generous, helpful people on here. I have an issue I was hoping to leverage your expertise to solve. This is a long post, but I wanted to include all possibly relevant info.

A few days ago, I was using the spa, and after I turned off the spa pump/heater, I heard some water trickling, which I had not ever noticed before. The next day, the water level in the spa had dropped significantly. The problem is that my spa water appears to be draining through a pipe that comes up vertically out of the ground, then has two 90-degree bends to point down. I never really noticed this pipe before, and don't know its purpose. The pipe the water is coming out of is about 50 feet from the spa, and comes out of the ground near the pool equipment.

Some clues/observations to help:
1. Water comes out of the drain pipe about the same speed as a faucet halfway on. The speed slows to a trickle, and eventually stops when the water level in the spa is at the level in the picture. If I refill the spa (or let the pool pump refill it through the pop-ups), the water starts to drain again.
2. The water level in the spa does not drain all the way down to the level of the pool, only about 8 inches down, then stops.The water level where it stops looks to be about the same height as the bottom of the upside-down U in the drain pipe.
3. The only way I can stop the water from coming out is to turn on the spa pump. Water stops coming out immediately when the pump is turned on, and starts again as soon as I turn the spa pump off.
4. Water comes out of the drain pipe in a big gush when I turn off the spa pump. This happens regardless of the level of the spa water--which makes me think that the drain pipe is some type of overflow or drain for the spa jets, or maybe the heater itself.

Background info:
-Pool has 2 pumps, one that runs water through the filter and re-enters the pool through a 6-port actuator to in-floor pop-ups, and a second pump that only circulates water from the spa through the heater and re-enters through the spa jets.
-Spa heater is a Pentair MiniMaxNT. No known system for bubbles in the jets; it appears to be water only.
-I've labeled the pictures with what I have gradually figured out does what, but there are still a few pipes I don't understand.
-The spa appears to have 3 drains in the bottom: one for the main pump, one for the spa pump, third one-?
-I haven't found any check valves in the plumbing.
-Have lived in this house for 2 years now; first time with this issue.

My questions:
A. What is the purpose of the U-shaped drain pipe?
B. Where does it connect from?
C. How do I make it stop draining/how to fix?

Thanks in advance for any help you can provide!
Spa Level.jpgPlumbing Pad.jpgSpa Heater.jpgDrain pipe.jpgAnother view.jpg


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Rocket J Squirrel

Silver Supporter
Bronze Supporter
Jun 7, 2018
Alamo, CA
Pool Size
Liquid Chlorine
Your mystery pipe looks like the spa air intake. With the spa running, you should feel suction there. If it's become waterlogged, I suppose it could be acting as a siphon.
Last edited:
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Reactions: Hodor


New member
Nov 29, 2020
Yuma, AZ
Thanks Mr. Squirrel! You were right. I was able to use a shop-vac to blow out the air lines. Not only did I fix my problem, but now my spa has air bubbles (which I didn't even know were built in!).
Thanks again, case closed.
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