Main drain or not

newgarage

Member
Jul 5, 2010
12
New York
I'm having a 20x40 vinyl lined concrete wall hard bottom inground pool 3 1/2-8' deep built.
I've been given recommendations by one builder for a main drain install(extra charge it is optional) and by another not to put one in.
Is this a must have or is it unnecessary? I know the new double drains w/hydrostatic valve and special cover are safe.
I'm concerned with heat distribution and filtering. The no main drain builder uses 3 skimmers, 3 directional return jets,
and 2 deep returns. The 2 deep returns are to provide deep water circulation. I was told by him that the main drain is really only for draining
and not that effective for filtering or heat distribution, draining below the skimmer height can be done with a pump.
Thanks in advance for any advice. I want to make sure I make the right decision.
 

Melt In The Sun

TFP Expert
LifeTime Supporter
Oct 29, 2009
3,899
Tucson, AZ
Where are you located? Main drains are difficult to winterize, but depending on your location that may not matter. It's also another hole in your liner, so another place to have a leak. I would get one regardless; you can always abandon it if you have problems, but you can't really add it later if you find that you want it.
 

tphaggerty

LifeTime Supporter
Jun 27, 2007
218
Poughquag, NY
Another consideration with an in-ground IF you are in a water restricted area - you will need a main drain if the water falls below your skimmers! That happens to me on occasion because we are in a community-well neighborhood and cannot use community water to refill. If we go for long periods without rain (and I forget to put the cover on, which reduces evaporation greatly), we can get close to the bottom of the skimmers. If you don't have a main drain, then you won't be able to filter (unless you jury rig a pipe out of the skimmer into the water) or you may wind up continuously sucking air. As was noted downthread, my assumption here was that you would have valves on the skimmers to be able to shut them off when the water dropped too low (but would then still be able to use the main drain)....

Maybe not a consideration, not something I would have thought of, but I'm sure glad that I have the main drain....
 

Little Aussie Battler

LifeTime Supporter
Oct 10, 2007
58
Sydney Australia
I just plastered in our main drain. It was old and with no cover and a sink plug was used over the hole. The pool cleaner used to get stuck on it. I used it once to drain the pool which is now in the process of a refurb. I still had to use another pump to get the last of the water out. There are other alternatives to drain a pool. If the water went below the skimmer I used one of the returns for a filter. As far as heat circulation, the main drain worked but it wasn't really worth the effort of turning the valves.
 

dmanb2b

TFP Expert
LifeTime Supporter
Apr 4, 2009
3,734
NY
If you are on LI. get the main drain. Have you gotten 5-7 estimates and checked with the builder's references? Yes a main drain may add a slight risk as it is another hole in the liner, but done properly, but with a 20x40 pool the benefits outweigh the negatives, especially with how much it cuts down on vacuming. Placed properly in the deep end, it will suck up debris and reduce the amount of dust, etc sitting on the pool bottom. LI tend to always have breezy conditions, so dust/debris will find it way into the pool.
 

ChiknNutz

LifeTime Supporter
Jul 22, 2010
145
Arlington, WA
Question on Main Drains...I have one in my pool, but when we went to drain the pool for the new liner install, once the water went below the skimmer, it would no longer drain (the pump lost it's prime and that was it). This must be by design, but is it typical? I thought that the main drain somewhat acted like a skimmer in that it would circulate water thru the returns as long as there was any water in the pool.
 

svenpup

LifeTime Supporter
Nov 18, 2009
835
Sacramento, CA
In order to drain below the skimmer you either need a valve to shut off the skimmer line while keeping the main drain open, or a Skimmer/Main Drain Diverter:





This is a "path of least resistance" issue and air offers less resistance than water.
 

geekgranny

LifeTime Supporter
Aug 20, 2009
1,358
North Central Texas
frustratedpoolmom said:
dmanb2b said:
Yes a main drain may add a slight risk as it is another hole in the liner, but done properly, but with a 20x40 pool the benefits outweigh the negatives, especially with how much it cuts down on vacuming.
I agree 100%
X2 :)

I love and appreciate the main drain. We have a lot of evaporation from wind/sun/heat. If left untopped up the water can get below the skimmer in a matter a couple of days. BTW... my old pool does not have an autofill. I've had two of the plastic auto fillers, hooked to hose, over the years. Their fail factor is too high to trust if one is going to be gone for a few days, with pool left unattended. But even built in auto fillers can "break".

Sometime a skimmer line can become clogged. It's really nice to have the main drain.

The main drain does help to distribute water, chemicals, warm/cold, better. It helps to keep the surface of my water less scorching in the summer.

Skimmer baskets can become clogged quite fast in fall, from leaves. I have two Pool Skims for fall/winter use, mainly because of leaves, and the skimmer basket becomes clogged in a matter of minutes with leaves. Of course the main drain can get clogged with leaves, if there are many, but you either turn the system off when you can't attend to the leaves or purchase or rig up a device that keeps leaves out of drain but allows water to flow. In my case it is a five gallon bucket, with big holes drilled in it, weighted, and a vinyl tube around small diameter poly rope to fish it out of pool with pool brush. The pool can get a foot or more of leaves in the bottom without causing restriction to the bottom drain.

Having had a only one pool, for many years, with lots of positive (and a few rare negatives) I can't imagine not having a main drain.

gg=alice
 

tphaggerty

LifeTime Supporter
Jun 27, 2007
218
Poughquag, NY
svenpup said:
In order to drain below the skimmer you either need a valve to shut off the skimmer line while keeping the main drain open, or a Skimmer/Main Drain Diverter:

This is a "path of least resistance" issue and air offers less resistance than water.
You are correct. SInce I have valves on both skimmer lines, I sort of assumed everyone would have them too! (Plus I have a valve on the main drain). As an aside, since it was brought up, I would also strong recommend that all of your suction lines have individual valves as well as each return. Can help greatly in balancing the water flow in the pool. In the spring, I shut down the main drain so that I get more suction on the skimmers to pull in pollen and other floaters - and like others, I leave the main drain partially open most of the time just in case the baskets get really filled up.