AG with drain on bottom

[Suarez7]

Hi all. I'm on the verge of closing a pool for the first time. I have a 37' round AG pool about 4.5' deep. I plan on boosting chlorine (clorox) and adding some algecide and then draining the water below the skimmer lines. My pool also has a drain on the bottom that gets fed to the filter. I'm slightly worried that the pipes will break during the winter, but haven't an idea how to keep water from getting in as its at the bottom. Anyone have that situation or suggestions? I don't trust pool store people. I'm in NJ so I assume water will freeze.

Thanks in advance for your help!

 

[X-PertPool]

You need to airlock the main drain. This is done by forcing air (most probably a shop vac) into the main drain until lots of bubbles start to come out of the drain. While the bubbles are coming out you need to quickly cap off the pipe either by quickly inserting a rubber plug or by closing a valve. Take some pictures of your setup.

Basically the whole idea is that by trapping air in the line water cant fill the line and bust it.

 

[Suarez7]

Thanks greatly X-PertPool.

I know the pool is a disgrace in terms of cleanliness currently! The pictures below are my setup. The main drain feeds from the bottom of the pool and comes up next to the filter. It's a pipe that I think could be left open throughout the winter. I am thinking about tying it (open) to the edge of the pool facing up and if the water inside the pipe freezes it will expand up and not crack the pipe.

Does anyone have a similar setup and has that worked?

Thanks in advance.

 

[X-PertPool]

It's really not the way you are supposed to do it, but you can try it. The water in the pipe facing upwards will definitely freeze; whether that will do damage is unknown. I don't think anyone really knows for sure what will happen to main drains if left "un-blown". In theory the maindrain line that runs above ground or near the surface will freeze and as that pipe extends into the ground the water won't be cold enough to freeze. So the expanding ice should push on the water going into the ground forcing the water pressure out the maindrain. Really who knows what happens in real life until they make a pool with a visible maindrain and you can actually watch what happens. I know in plumbing they say pressure from the water will crack a frozen pipe and not the ice itself from expansion. I'd be worried that freezing ice in the pipe could get hung up in a section and end up freezing and cracking the pipe before the excess pressure has a chance to exit through the maindrain. I could be totally wrong on this though, I think you still have to factor in if the maindrain line starts to freeze near the pad and pressure wants go towards the path of least resistance will it be the maindrain in the bottom of the pool? Keep in mind that there is a lot of pressure at the bottom of the pool pushing back on that expanding ice; maybe this is how things get damaged.

Regardless, maindrains on above grounds are about the only time I saw a maindrain actually be useful. It seems in a round pool you can direct the return line to cause the water to sprial in the pool and this causes any sinking debris to end up right in the center of the pool, right where the maindrain is at. It's almost self cleaning.