My car is plumbed just as the good Dr, says, Before you install, this is the time to make sure it is working as it should. To test the valve block off the small port and hitch up your Mighty vac. or your brand hand vac. pump to the large side and create a vacuum and then release using the vent on the gun. The valve in the top of can should allow the can to hold vacuum, this also will test the structural integrity of the can to make sure you aren't creating a vacuum leak by installing.