Or at least the new ones do, thanks to the .gov and and EPA CARB laws. If you haven't had the displeasure of using one of these new pieces of total fugtard crap, they have an "automatic" vent and flow shut off built into the filler neck / spout. You cant buy an old school one new anymore.
There's a problem with these things, THEY DONT FUGGIN WORK! They were intended to be safer, and reduce fuel spills. But instead, they dont vent, at all -EVER! They typically spill more fuel on the ground than they do into the device your attempting to fill, and good luck at the filling station when you unscrew the Frankenstein filler/vent nozzle off the plastic can and try to dispense gas into it since there is no other vent hole on the back side.
Thats right folks, the EPA mandated something be made unsafe, in order to make it safer!
So there's money to be made here people, we simply market a "water fill nozzle and vent cap" that requires you drill a small hole in the plastic can for the vent to thread into, and the main filler neck will have the same factory thread as the can. Jut like the good old fashioned one that worked perfectly, this will retrofit the EPA cans and allow them to actually do what they are intended to do.