Main Drain Plumbing

jparr

Well-known member
Jun 12, 2010
65
My 20,000 gallon plaster pool was recently refinished by our pool guy, and he filled in the main drain because he said it was leaking and couldn't be fixed. I have since taken over the pool and maintain it myself, and am trying to figure out the main drain issue. There are two 1.5" pipes teed in to the inlet side of the pump, and if I shut off the valve on one, nothing happens, shutting off the valve on the other starves the pump. This is consistent with the main drain being plugged up. I dove down and removed the cover from the drain to vacuum out some crud that had collected in there, and found that there were two 1.5" pipes plumbed in to the drain. One appeared to have gone straight down, and is packed full of concrete, this must be the one he blocked due to the supposed leak. Then there is one that appears to run horizontal rather than straight down. I was able to push a screwdriver in about 10" without feeling any resistance or cap. Any idea what this could be? Is there a chance two lines were plumbed to the drain? I have heard of this being done, but couldn't find it anywhere near the pump pad.
 

PoolGuyNJ

TFP Expert
May 20, 2007
3,192
South Central NJ
The drain isn't plugged from the work. The drain is plugged from the underside of the pool.

If you have hydrostatic plugs in the hopper, don't sweat it.

If it was a hydrostatic valve in the drain, now we have a problem, bigger if the pool doesn't have hydrostatic plugs too. If the water table is high and your pool level drops significantly, such as when CYA gets too high and dilution is needed, upward hydrostatic pressures will be exerted on the shell bottom.

If it's a worst case scenario, clearing the concrete and properly replacing what was needed will have to be done underwater. Can't empty the pool with a high water table.

Scott
 

jparr

Well-known member
Jun 12, 2010
65
PoolGuyNJ said:
The drain isn't plugged from the work. The drain is plugged from the underside of the pool.
It is most definitely plugged from the work. He informed us that he plugged the leaking drain, and when I pull the cover off, the pipe that leads downwards is sealed up with the same color plaster as the pool.

PoolGuyNJ said:
If it was a hydrostatic valve in the drain, now we have a problem, bigger if the pool doesn't have hydrostatic plugs too. If the water table is high and your pool level drops significantly, such as when CYA gets too high and dilution is needed, upward hydrostatic pressures will be exerted on the shell bottom.
Yes, this is what I became worried about after reading about hydrostatic valves. Our water table is quite high.

Would a downward plumbed pipe *always* be a hydrostatic valve, and the horizontally plumbed line always be a return to the pump? If this is the case, I'll just live with the closed off hydrostatic valve, and focus on clearing the blockage in the return line.
 

PoolGuyNJ

TFP Expert
May 20, 2007
3,192
South Central NJ
Yes. Hydrostatic valves and plugs always face down.

If the hole going down is plugged and the one on the side isn't, I can almost guarantee the drain is open for business.

Whether the downward hole was a hydrostatic valve or just a clean out plug not properly sealed in the drain pot is the $64,000 question. Clean out plugs are plastic pipe plugs. Drain pots typically have two ports available for use. The one on the side is normally used to connect to the pump when the pot is on the floor of a pool.

The one on the bottom of the pot is frequently used as a hydrostatic plug or is removed and a hydrostatic relief is threaded in.

When it's used as a hydrostatic plug, it may have been installed a little loosely and leaked. They normally are untaped if if not checked before installation, will make you pull your hair out wondering where the water is going.
 

jparr

Well-known member
Jun 12, 2010
65
Update: Re: Main Drain Plumbing

Manged to clear up my main drain clog today. Shut off the valve for the skimmer, leaving the drain isolated to the pump. Removed the pump basket cover, and inserted a homemade drain king in to the intake plumping, and blasted away. A golf ball shot out of the drain in the pool, followed by a **** of a lot of old DE. The pump seems to be working much easier now (a bit quieter, sounds less strained).
 

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