At least with Mercury’s EPA tanks, they use something called a demand valve. It’s actually made by Attwood, too. It goes inline between the tank and the primer bulb. The idea of it is that it will withstand high fuel tank pressure but not open until the fuel pump on the engine creates a negative pressure in the fuel line. These are especially important when you tip the motor up and the float valve may not be as effective in shutting off the fuel.
https://www.ebay.com/itm/273375882259?epid=1218878583&hash=item3fa678ec13:g:52IAAOSwD9pbWzZ-
Long live American manufacturing!
