How To Test for Air Leak? (found - tree root grew into line!)

Thanks so much, Waste
We were told to not use the one valve (the line that he fixed) until this morning because of some adhesive he used. So this morning, I turned on the pump and very slowly started opening that second valve, when all the sudden I started see air - lots of it, and then starting lose the prime on the pump. So I immediately closed that valve, waited for the basket to fill, and then tried again. This time it worked perfectly and the water in the basket is as clear as a bell with NO air bubbles :D I even checked again before I left for work just to make sure.

Thanks again :)