All the gas tank emissions stuff is gone, so I repurposed this air filter canister and breather snorkel thing that originally had a bunch of solenoids, charcoal canisters and junk attached to it. I tested the gas tank vent (The big one, not the tiny vent that is connected to the filler cap) and it has a rollover valve already built into the tank along with some nice baffles. There is no need for an external rollover valve or anything, just a way to let air in and out of the tank.