Many chemical companies sell de-foam Nalco , Baker are two 10 qts a day to start down the casing , if you run a 3/8 stainless tubing down the casing to the pump inlet is best, but pumping down the casing can work, Diesel is a poor boy way of knocking down foam . Batch about 20 gals down the casing and watch the pump kick ass for awhile that will tell you if the de-foam would help .