Main drain and where does this skimmer pipe go?

8ightiesfan

Active member
May 26, 2020
31
Canberra, Australia
Still on the learning curve of pool ownership. I have well balanced pool water now thanks to this forum but now trying to learn about a few plumbing areas of the pool.

I read a few threads on here about main drains, hoping to learn about how mine works. There is a blocked off pipe in my skimmer, I assumed it goes to the main drain but now I am not so sure. I removed the cap and nothing happened so I attempted to apply suction to it by installing the skimmer plate and I placed a rubber ball on the top so the suction was forced from this pipe only. What came out in the space of 10 seconds was pretty gross (see pic). I emptied the basket and went again but nothing more came out and it is nice and clear the second time.

But my question is this, does this pipe lead to the main drain? How can I check this? I remember during the initial pool handover that the pool guy said the main drain was a hydrostatic valve and said it would allow water to enter the pool if there was sufficient water beneath it to stop the pool from popping out from pressure. Does this mean there is no pipe up to the skimmer and the main drain just goes into the earth below? If so , where could the capped off pipe in the skimmer lead to?

Cheers
 

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HermanTX

Gold Supporter
May 20, 2020
783
Katy TX
Do you have 2 skimmers or 1? The purpose of the second hole on the skimmer is to draw water from main drain (assuming that is where it is connected to) to ensure your pump does not run dry if the level of water goes below your skimmer or - as it appears in your picture showing the second hole on the side above the basket, if the basket becomes so full that water cannot flow through the basket then the second port allows water to be pulled from the bottom (again assuming it is connected to the main drain). So if you have 2 skimmers, it would be expected that 1 is active (the second port is connected to something) and the other skimmer has the second hole plugged off (like your picture). No need to have both skimmers plumbed to the main drain as that is just redundant.
Alternatively, if the second hole is NOT plumbed to the main drain - it may have a line to the side of your pool - may look like a return but is there to be the suction point should the water drop below the skimmer level.
The third possibility is that It could also be that neither (if you have 2 skimmers or 1) is connected to the main drain and that second hole was just plugged off on both (or on the only) skimmer. So if your water level drops below the skimmers then your pump will start to cavitate because it is sucking air. That may be done like that if the pool has a autofill feature, in theory, your water would not drop therefore you do not need the second holes in either skimmer and both are plugged. As you can see, there are many different scenarios that you can consider and report back to the forum.

The comments from the PB on the hydrostatic valve on the main drain is as he says and that is good you have that but unlikely related to the skimmer. BTW - how old is your pool?
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
19,495
Bedford, TX
8,

Show us a pic of what is below the skimmer basket...

Also show us a pic of your equipment pad, especially what pipes come into the suction side of your pump.

Some main drains have a hydrostatic valve, but it really has nothing to do with how the main drain itself operates.

Thanks,

Jim R.
 

8ightiesfan

Active member
May 26, 2020
31
Canberra, Australia
To answer a few questions

I only have one skimmer
I will post a pic of under the basket but it has one exit which leads to the pump
There is no auto level device fitted
Pool was built around 1992
The capped of pipe in the photo is what I am trying to work out where it leads to
Can it still lead to the main drain if the main drain is hydrostatic?

Thanks!
 

8ightiesfan

Active member
May 26, 2020
31
Canberra, Australia
Here is a photo of under the skimmer basket, just the one return to the pump, and a pic of the equipment pad. There is only one return to the pump so I don't believe the capped off pipe leads to the pad

I believe now that the blanked off pipe in the skimmer DOES lead to the main drain which is also a hydrostatic main drain. Does this assumption seem correct?

If this is the case, should it be capped? Is there any advantage in removing the cap? When I remove it no water is sucked from it and no air escapes so I don't think it would aid pool water flow by removing it.
 

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Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
19,495
Bedford, TX
8,

With only one pipe into your pump, then you are correct that the main drain is not plumbed back to your equipment pad.

I too would "assume" that the main drain is plumbed into your skimmer. That said, I have never seen a skimmer like yours and have no idea how it works.

I have two rent house pools that have no operational main drain and they have worked just fine for over 10 years. There is really no reason to even have a main drain.

That leads me to the question... What do you think a working main drain is going to do for you???

Thanks,

Jim R.
 

8ightiesfan

Active member
May 26, 2020
31
Canberra, Australia
Hi Jim, only benefit I thought was I have read that some main drains also act as a return and help keep the floor of the pool cleaner and to improve water circulation. Other than that I just wanted to confirm how I thought it was plumbed simply to understand how it works better.
Cheers