Metal gas cans should be vented for safety. If theyre exposed to fire conditions, they could build up pressure and explode. While plastic cans can benefit from venting as well, they can be expected to melt in a fire, as opposed to exploding.

Once your gas can is emptied out, you can wash it with water and dish soap. But, to avoid getting water in your new fuel, allow it to dry completely before filling.

Type I safety cans only have 1 opening which you can pour & fill from the same opening. Type II safety cans have 2 openings, one for pouring and one for filling. The fill opening serves as a vent for the evaporated gas when pouring.