BOB - Blow Out Button clears the dip tube in aerosol cans.
Whenever you stop spraying, turn the can upside down and depress the nozzle until nothing is coming out except clear propellant. The propellant forces any remaining finish out of the dip tube and nozzle before it dries, keeping it clear for the next time.
Use the Blow Out Button (BOB) for dip tubes that are hard to clear out.
Replace aerosol buttons (AB) when they become clogged.