They have a hose that hooks up to the return line side of the tank. You put the return line hose in a bucket, hook the hose up to a compressor, pinch off the overflow vent hose, and turn the prop like your trying to burp the system. Once you start seeing oil pumped into the bucket your done. Remove the hose, replace the return oil line to the oil tank, and your system is purged. I have a hose sitting on the shelf I could loan you.