Well, I think I have a leak in my main drain line somewhere. The shot below is my pump and the valve that switches between the main drain and the skimmer. Near the ground of both lines you'll see a check valve, one of them with the see-through window - that's the main drain line.
With the pump running, if I shut off the main drain line, you see nothing. If I shut the pump off, it stays good. However, as soon as I start opening that main drain line, you start seeing bubbles flowing through the see-through valve in a stead stream. You can hear almost a trickling down in the line as it goes underground as well. Below the check valve, the place I had close the pool last year drilled a plug so they could fill it with antifreeze or something. I checked it with shaving cream and didn't notice anything. I was able to tighten almost a half turn but it didn't seem to change anything.
So, my feeling all along has been that if the system was airtight like it's supposed to be, I shouldn't be getting air bubbles flowing through that check valve and water leaking. For that matter, I'm not quite understanding why, since this is a check valve, air is escaping up and water going down anyway (educate me please).
Anyway, to sum up, looks like there is a drain somewhere below the check valve, assuming the check valve is operating properly. Is that a rational conclusion? And how in God's name do I find it? Does it sound like I one of the lucky ones who got a below ground leak?
Thanks for any help you all can offer...