Enviro-Safe ProDry contains a dehydrating agent that converts system moisture into oil. We recommend the use of ProDry before the use of Enviro-Safe ProSeal to ensure all moisture has been removed from the air conditioning system. ProDry comes in 4 ounce aerosol, 8 ounce concentrate and 1/2 ounce Vacuum Sealed cans. The 4 ounce aerosol can connects to regular system with a 134a tap #5000.