Abstract: A degassing and water removal apparatus is used in combination with the testing or replacement of dielectric oil in an RF transmitter. The apparatus comprises at least one ultrasound transducer in vibrational communication with a bulk oil sample held in a tank having a reduced internal air pressure. The tank has fluid connections to the RF transmitter through which oil from the transmitter is drained to the tank and through which the ambient air pressure in the transmitter is reduced. A fluid pump is used to pump the oil from the tank back to the RF transmitter. In a method of using such an apparatus, the RF transmitter is held at reduced internal pressure during the return of oil thereto, so that the oil does not dissolve gases in the atmosphere internal to the RF transmitter.