Main Drain Line Leak

dpcory

Member
Sep 2, 2014
17
South Bend, IN
I have a 40 year old concrete pool with fiberglass panel walls. I have separate skimmer and main drain lines. The pool is surrounded by a concrete apron and there is also a brick patio (with concrete underlayment) in between the pool and the equipment room. I believe the main drain line is black ABS.

I've owned the house for 5 years. The first 3 summers, the main drain worked great. Towards the end of last season, there appeared to be a small leak that developed somewhere in the main drain line. I closed the pool as I normally would last fall. This spring we had some torrential rains before I opened the pool (I have a mesh cover). Despite the heavy rains, when I took the cover off a couple weeks later, the water level was low--essentially right below the skimmer. This season, I have only used the skimmer line but have tried out the main drain line a couple of times. Yesterday I blew the line out from the pump side with an air compressor to be sure there was not an obstruction in the line. Water pushed through easily and was bubbling strongly up from the drain. After confirming no obstruction, I turned the pump on, shut the skimmer line valve and left the main drain valve open. I can see water in the pump moving up and down and occasionally looks like it might go "whoosh" but never does. The instant I open the skimmer line, I get full suction pressure. So, the apparent leak is significant enough to prevent the pump from maintaining suction when I have the skimmer line shut off and rely solely on the main drain. But it's not significant enough to cause an issue when I have both lines open. But I've kept the main line closed all season, relying solely on the skimmer line, which has been fine. But I want to figure out a plan for the main drain.

I have a couple of questions and am looking for some input on my options. As I see it, they are:

1) continue doing what i'm doing - filling up the pool a couple of times a week to make up for the lost water, leave the main line open but don't use it;

-Does the fact that I am continuing to lose water despite not pumping any water through the main drain line indicate that the leak is somewhere deep, close to the drain itself? If the leak is
up closer to the surface, I shouldn't be losing water if I'm not pumping water through that line, right? If the leak is low, I would have expected the water level to be much lower in the spring
after a whole winter of losing water.

-Will I be able to keep water out of the main drain line when I close the pool? Doesn't a leak prevent me from achieving an air lock? Will the problem just get worse? Does the fact that it's
ABS pipe make any difference?

2) eliminate use of my main line altogether by installing a plate over the drain;

-If I eliminate the main drain, do I need to do something to get the water out of the line? Will a shop vac from the pump area do it?

-Assuming I am able to get the water out, do I need to do anything with the main drain line when I close or open the pool in the future?

3) contact a leak detection service to try and identify the area of the leak and repair it - or hire someone to repair it;

-I'm assuming that the leak is going to be somewhere under brick and concrete, and so the repair will cost at least $3-5k. Is it worth it to have a main drain when my skimmer works perfectly
well?

4) try installing some type of liner with a bladder.
-Has anyone had good or bad experiences with these? Does the fact that my line is ABS pipe with connectors make a difference?

I know that's a lot of questions but really any input on any of these topics is greatly appreciated as I consider my options.

Thanks in advance.
 

NewPoolGuy#1

Member
Jun 15, 2017
6
Wisconsin
I am interested to hear what people say about this, I have been running off the skimmer alone for years. The old owners actually relined the pool and covered the main drain.

Sorry i can't be more helpful, but good luck!

J
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
12,871
Houston, Texas
If you are losing water with the plug in the main drain or are you cutting off flow at the equipment pad? If you are using the valve at the equipment pad to cut off flow to the main drain, then yes it can still leak. If you install a plug in the main drain and the leak stops then the leak is somewhere in the main drain plumbing.

You can operate a pool just fine without a main drain, not every inground pool is built with main drains.
 

PoolguyinCT

In The Industry
Jul 21, 2014
3,077
Connecticut
Post a picture of your steps or ladders.. I am very familia the pool package you are describing. I’d like to see some stamped branding, but I am confident I know this kit well enough to land this.
 

dpcory

Member
Sep 2, 2014
17
South Bend, IN
I am cutting off flow at the equipment pad, have not plugged the main drain yet. I am 99% sure that the leak is in the main drain line because I don't know how else to explain the lack of suction, now that I've confirmed there are no obstructions in the line.

I will post some pics of the steps and ladders later this evening. It's a rectangular pool with steps at the corner. I should have added to the post that I had leak detection guys out to check for leaks previously. There was a loose ABS connector for the main drain line at the equipment pad at the time (it has since been replumbed) so unfortunately they weren't able to actually determine if there was a leak in the line below ground. But they went around to the pool light, steps, etc. and did not detect any leaks. There is a pretty significant bow to one of the fiberglass panels next to the steps and it has a visible crack, which has been sealed. I have always suspected that this crack leaks water but have dye tested myself and had the leak detection guys check and it does not appear to leak. And, as I said above, I am 99% sure that the leak is in the main drain line because it won't hold pressure and I don't know how else to explain that.

Pics to come......

Thanks,
Dan
 

dpcory

Member
Sep 2, 2014
17
South Bend, IN
I talked with a pool guy in my area and he suggested going down and putting a black expanding plug in the main drain line to confirm that's where the leak is before going to the trouble of putting a plate over the drain. I'm going to go ahead and do that. Can I just leave that plug in there all winter? What should I do to close the main drain line given the leak?
 

dpcory

Member
Sep 2, 2014
17
South Bend, IN
The pool company doesn't do leak detection themselves - they suggest a leak detection specialist. And they charge $295 per visit. Apparently business is good.
 

PoolguyinCT

In The Industry
Jul 21, 2014
3,077
Connecticut
The pool company doesn't do leak detection themselves - they suggest a leak detection specialist. And they charge $295 per visit. Apparently business is good.

That’s actually reasonable, if they are well equipped & competent. You style pool is usually a group of small leaks.
 

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dpcory

Member
Sep 2, 2014
17
South Bend, IN
I went down and put an expandable plug in the main drain and continued to have water leaking. The crack in the fiberglass panel (shown in the pics linked above) appeared to be the culprit. I pulled off the old patch and put a bunch of A+B epoxy putty to fill the crack all the way down. That resolved it. But now I'm left unsure of whether the main drain line was leaking at all or it was all from the cracked panel. Since I clearly have a leak in the main drain line, it doesn't really matter where it is until I'm ready to hire the leak detection guys again. However, if the leak is well above the water line, close to the equipment pad, I might try to dig down to it from the pad and try to replace the broken pipe / leaky connection myself (the pad was broken up years ago and is just dirt, in an enclosed pump house).

I should probably just be happy it's not leaking and not worry about the main drain line for now. But what fun would that be?
 
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