Usually marked vent, vacuum and purge.
Vent to the gas tank and on newer 720s also to the carb vent to collect boiled off gas after shutdown.
Vacuum. Anywhere on the intake to suck fumes stored in the charcoal.
Purge is just a vacuum signal to say the engine is running and allows intake vacuum to empty the canister. Usually from the ported vacuum advance so it only operates above idle and when the engine has warmed up.