The thickened transparent hose allows you to observe the coolant flow. One end of the hose is a brass quick-plug and the other end has a fine filter to isolate impurities. 【Quickly Remove Air and Refill Coolant】 This cooling system vacuum purge & refill kit draws a vacuum on the entire cooling system, quickly removing trapped air to ensure no air pockets are left when refilling and monitor pressure gauge readings under vacuum to uncover leaks.