Abstract: A system and method for testing the oil in a transformer, comprising attaching a threaded shaft to the wall of the oil tank at a height sufficient to avoid the sediments that accumulate on the bottom of the oil tank, drilling a small hole through the stud into the tank, attaching a ball valve to the stud, and filling a double-ended glass vial through the hole. The double-ended glass vial preferably comprises a cap with a tapered barbed stem incorporating a shut off valve that can be connected to the ball valve port by means of simply processing the tapered barb stem into the ball valve port.