I'm a first time pool owner in Nebraska (hard freezes, frost line 3 feet). My wife and I just bought this house in July, and it came with a 20x40' doughboy above ground pool. The pool has a 'deep end' 6 feet deep, with a bottom drain. It's now about time to winterize, and I wanted to get some input on how to do this for this pool. Reading some other threads (including this one) about winterizing AGPs with bottom drains, I think this pool is a bit different, in that the bottom drain is not close to the pump. The bottom drain is in fact at the opposite end of the pool from the pump, It first comes up out from under the deep end, and up a U-trap a couple feet above the ground. at the top of this is a valve. Then it runs about 30 feet alongside the pool under the deck, then there is another valve, right before a Y connector where the skimmer joins (the skimmer has it's own valve, so you can operate just the skimmer, just the bottom drain, or both), and then the pump connects on the 'base' of the Y connector. Here's a couple pictures. The first one is looking toward the deep end wit hit's trap in the distance, and second photo is of that trap.
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I don't think I can raise the end of the Y connector high enough above the water to be able to just pour in antifreeze. Based on the U trap with valve at the deep end, I was thinking maybe the best solution would be to blow air into the line till bubbles come out the drain using an adapter like what Garrybunk posted above. Due to the U trap, this would mean that the pipe on the pool side of the trap is full of air entirely, until the very bottom below the drain, which is at least a couple feet below the dirt, not to mention below the pool itself. After filling the line with air, I'd close off the trap valve, trapping the air in that section. Then I'd simply gravity drain the line on the pump side so it would also be empty. I do have an air compressor that I regularly use at 120psi for air tools. Anyone have an idea if this is enough to force out 6 feet of water pressure?
The other thought was to maybe get a piece of hose to extend from the Y connector high enough to be able to pour in the antifreeze. But my concern there is in order to get antifreeze all the way to the drain I have to overcome that U trap. This will take a lot of antifreeze. Then in the summer I'd be blasting all that stuff out on the lawn, and I'm on an acreage with a well, so I'm kind of sensitive to pouring chemicals on the ground. I've read that antifreeze can contaminate groundwater.
The weird part about all this is that the U trap was not closed when I opened the pool in July. It was wide open. So the previous closing of the pool did not utilize the trap. When I first ran the bottom drain I ran it to waste, so I'm not sure if it was full of antifreeze or what. Due to my ignorance and the idiocy of a couple people from the pool store, the opening itself was a disaster that dumped all the winter leaf litter from the cover into the pool, so I could not see the bottom drain when I first ran it, to see if there was any antifreeze showing. A big thanks to everyone at TFP btw. These forums got me through a really disastrous pool opening, and very steep learning curve.
So ya, right now I'm leaning towards the air method, but wanted to get some other input. Thanks for reading this rather long post, and I hope piggybacking on another thread of the same subject was ok.