should I and how to plug the main drain

[sdtfp]

I've been opening and closing my pool for a few seasons now and I assumed my main drain was open. I didn't live here before that and I don't recall how the previous owners closed the system. Recently I dove down in the pool with goggles and saw a rubber plug in the main drain.

The way I normally close is that I blow air through the suction line pipe where it connects to my pump. I have an anthony/sylvan style pool with a two tier plug for the skimmer because the main drain and skimmer are on the same line with a "T" to the pump (See attached diagram). With two people I first blow all the water out of the skimmer and push the two tier plug down 1 tier. Then I keep blowing out to the main drain for a good 1 minute of air bubbles and then plug the suction line at the pump. IT never made too much sense to me, so maybe that is wrong but I haven't had issues. If the main drain was plugged this whole time then I should not have seen any air coming out of there when closing, so I must of forced the plug out and its just gravity keeping it there or the suction when I open up the pool.

So my question is, should I have the main drain plugged? And do I need to plug it while air is coming out of it? So dive in and have someone push air from the suction line in the pump? I assume this is the "right way" because if I don't do this and just plug the main drain without forced air, then there will be water in the pipe between the skimmer and the main drain. I don't want that right?

And let's say I do it the "right way" with forced air, then if I run the pump after that then the air in the pipe between skimmer and main drain will be pulled out and replaced with water. So in fact, there is no way for me to plug the main drain without leaving water in the pipes. So it makes me think that maybe I need to remove the plug on the main drain so that I can close it with forced air, as I believed I was doing. Also, I still don't really get how air just doesn't escape up out of the main drain after I force air in and plug the pump side. Maybe I've had the wrong idea of what is going on this whole time. What should I be doing?

 

[Newdude]

Many main drains have 2 ports.



My 'bottom' one is plugged and it pulls water from the side. Or a hydrostatic valve may be installed in the other port.

When you close, you only need to force the water in the drain pipe below the frost line (2 to 3 ft for us) and then 'air lock' it by closing the valve or plugging it at the equipment pad. It acts like putting your finger over a straw and the bottom water can't force its way back in to the water level of the pool. At 5 to 8 ft deep depending on the pool, it'll never freeze down below.

 

[sdtfp]

Many main drains have 2 ports.

View attachment 521499

My 'bottom' one is plugged and it pulls water from the side. Or a hydrostatic valve may be installed in the other port.

When you close, you only need to force the water in the drain pipe below the frost line (2 to 3 ft for us) and then 'air lock' it by closing the valve or plugging it at the equipment pad. It acts like putting your finger over a straw and the bottom water can't force its way back in to the water level of the pool. At 5 to 8 ft deep depending on the pool, it'll never freeze down below.

Yeah I don't have a bottom side like you do. So I can't plug the main drain on the skimmer without also plugging the skimmer.

Good analogy on the straw. So in your case you can do that and plug it in the skimmer and/or the bottom of pool drain. But in my case, I cannot plug the main drain in the skimmer without plugging the skimmer. So I would need to plug the drain in the bottom of the pool I think. But then water will remain in that line all the way up to where it "T"s with the skimmer pipe. Which i doubt its 3 ft below the soil.

 

[Newdude]

But in my case, I cannot plug the main drain in the skimmer without plugging the skimmer

Install a gizmo and blow from the pad. It'll effectively be a straight shot to the main drain. Then air lock the valve at the pad.






No two pads are the same so post a pic and we can see if we can hatch a plan.

 

[sdtfp]

Install a gizmo and blow from the pad. It'll effectively be a straight shot to the main drain. Then air lock the valve at the pad.

View attachment 521506


View attachment 521507

No two pads are the same so post a pic and we can see if we can hatch a plan.

thanks the illustration helps! I think I am following on how to get it winterized. But am I correct in assuming that I need to remove the plug on the pool floor drain? I guess that is the root of the confusion. Why did they have that plugged if it does not add anything and in fact, with it on you cannot properly winterize the system because you cant get air to flow there.

 

[Newdude]

But am I correct in assuming that I need to remove the plug on the pool floor drain?

I'm not sure it's as you think. If you were plugged firmly, you wouldn't be able to blow bubbles when winterizing. If you blew the plug out while doing so, then you're no longer plugged. That's why I think there's another port down there that you didn't realize at the time.

Why did they have that plugged if it does not add anything

Most plug the main drain when there's a leak in that line, so they don't have to fix the plumbing under the pool.

with it on you cannot properly winterize the system because you cant get air to flow there.

If it is in fact plugged solid, you'd lower the water below the skimmer, blow out the pipe to the equipment pad and snake a garden hose down as far as you could to suck out the main drain line below the frost line. Then you would gizzmo the skimmer to keep it from filling over the winter.

 

[sdtfp]

I'm not sure it's as you think. If you were plugged firmly, you wouldn't be able to blow bubbles when winterizing. If you blew the plug out while doing so, then you're no longer plugged. That's why I think there's another port down there that you didn't realize at the time.

Most plug the main drain when there's a leak in that line, so they don't have to fix the plumbing under the pool.

If it is in fact plugged solid, you'd lower the water below the skimmer, blow out the pipe to the equipment pad and snake a garden hose down as far as you could to suck out the main drain line below the frost line. Then you would gizzmo the skimmer to keep it from filling over the winter.

I think I was plugged in firmly until I blew it out because the grate over the plug looks brand new but it's missing one screw. This makes me think I violently blew out the plug a few times and it broke one of the screws on the grate off. I have the cyclone blower.

I like the idea of pluggin it and then using a hose to suction out the line. What kind of pump do you use for that? I have a water pump but it doesn't have a suction side hose connection. Do I need somethng like Amazon.com ?

I also want to know what kind of plug is usually used on the main drain? It currently has the standard black rubber plug. I am nto a big fan of those as I have some that are disintegrating on me. Is there a better options for a main drain plug?

 

[Newdude]

I like the idea of pluggin it and then using a hose to suction out the line. What kind of pump do you use for that?

I stick the dry end of the garden hose up the shop vac hose and duct tape it sealed. It only takes 2 or 3 wraps to seal it up.

You'll have to dive down and fix the plug or else you'll suck the pool too.

I also want to know what kind of plug is usually used on the main drain?

Modern models have threaded ports so a pvc plug can screw in. Smooth ports need an expandable plug.

This makes me think I violently blew out the plug a few times

You only blew it out once. Then it bounced around the cage with force like a lottery ball.

And now I agree. A cyclone would likely pop an expandable plug with ease. It hasn't been plugged since your first close. I'm surprised you never noticed a leak as the likely reason it was plugged. It's also possible the last owners were afraid of it somehow, and plugged it out of abundance if caution.