how to use fix a flat tire sealant
1 Screw the can of Fix-a-Flat onto the valve stem, you'll hear it start to fill the tire with air. 2  When it stops filling, unscew the can and replace the valve stem cap. 3  Drive the car right away.4  The sealant in the magic can needs to circulate evenly inside the tire to fill the leaky hole and ride evenly.et ready to save the day: 1  Pull over to a safe area. 2  Remove the black cap from the valve stem (the nipple that the air comes in through). 3  Put the cap in a safe place, you'll need to put it back on when you're done.*. 4  Screw the can of Fix-a-Flat onto the valve stem, you'll hear it start to fill the tire with air.