I have a pool with leak in skimmer back to the 3way in front of the pump.Skimmer pluged no water loss. Take plug out and water runs out in 1min. Now I charged the system and can only get about 7-8lb max. Tried to put air in the high side
and water in skimmer. Can hold pressure with water on and air on. Cannot pin point leak with xlt30H . sometime I hear water rushing, but weak in sound. Large leak I know any suggestions?

I've had luck on large low pressure leaks by using 0-30 gages and finding the sweet spot where the gage needle bounces. Try playing with with water and gas flow volumes. More often than not I use lots of gas to find low pressure leaks.
hap

Put your water and air in from the pump end and listen at the skimmer. It may be a cracked fitting right below the skimmer. Or try filling the pipe with water then, with the skimmer plugged, try blowing it out with air while listening underground.

Sounds like the plug in the skimmer was closing the crack where the skimmer meets the pipe. I know the post was from a while back but would be great to read the outcome texanstar.

Plug the skimmer with a threaded SP1022-C Hayward winter plug to make sure you are not extending your expansion plug into the fitting and sealing it off partially!