Before screwing on the valve stem cap, spray the stem tip with window spray cleaner. If you see bubbles, then you have a leak. I repeat the spray and look two or three times. The fools that change tires SHOULD spray the rim with soapy water INCLUDING the rivets inside the wheel where the center joins the rim, then around the inside and outside of the beads, then finally in and around the valve stem. Windex works as good as anything to create bubbles. If a tire man is in too much of a hurry to do this procedure then surely he is in WAY too big a hurry to reach for my cash.
