Abstract: A device and method of using a liquid/air pressure testing tool to assist in testing and repairing liquid-filled agricultural tires is herein disclosed. The device provides a valving arrangement to allow alternating fluid transfer and air backfilling of a fluid-filled agricultural tire. The device utilizes quick-disconnect fittings providing quick in-line installation therebetween a fluid pump and a fluid filled tire. The device provides an inline ball valve and an isolation valve, thereby providing isolation of a pumping source and an air back-filling means, respectively. During fluid filling of a tire, the isolation valve allows monitoring of internal tire pressure using a common pressure gauge without removing the device or disconnecting any attached hoses. The device thus eliminates repeated steps when testing or repairing large fluid-filled tires as used on farm tractors and other agricultural machinery.