Lock the vent cover permanently in position by inserting and fully tightening the grub screw followed by the Atkinson Shear Screw, which snaps off when tightened, leaving nothing proud of the surface that can be used to remove it.

The temperature inside a tank can change due to the weather and different seasons, as a result the inside of the tank expands and contracts. Installing a vent cap allows the tank to breathe safely without damaging the inside of the tank.