I think that automotive antifreeze would be just fine, however it is a toxic liquid and proper disposal might be difficult. RV antifreeze at Walmart is currently $3.48 per gallon, it was $3.00 a couple months ago. I used the RV antifreeze in my sprayer last fall and there was mold in the tank in the spring, if you use it like that the tank will need to be dried thoroughly.Automotive anti freeze is good for the seals in an engine, but not for seals in a P/W pump?