[LH Lead-Foot]

I may have to read the post again but using a late model carbon canister, factory purge valve is the best option for during fuel fumes you paid for. Also, this will keep higher pressure build up in the tank that helps during refueling and keeps the hydrocarbons stored. The canister has three connections, purge goes to the engine the opens during highway speeds with warm engine. The PCM will take charge of this operation via pulse width modulation, while monitoring the o2 sensors to keep it from running rich or lean if canister is empty.
The vent connection is normally run to a solenoid that is normally open, until the PCM's clock says it's time to run an EVAP test. That's the only time the vent is closes. During refueling, the vent is open to allow hydrocarbon rich air to pass out thru the canister to allow it to capture the hydrocarbons. If equipped with a third connection, that says tank, this goes to the fitting that has an "Roll-Over" protection device or called a vent check valve. When liquid hits it, it simply closes and backs up fumes in the tank and liquid fuel backs up into the filler neck to shut off the gas pump via the aspirator tube inside the nozzle.

If you have an aftermarket fuel pump assembly and tank, depending on the piping, one should be there for vent. Aftermarket pumps usually don't come with a vent valve, so one can be added on the outside.

A tank fitting marked vent, can be used to solve two problems. If the pump has piping marked vent, a hose would normally go into the filler necks little pipe near the top, if that is what you have. The hose that goes from this little pipe back into the tank fitting can have a "Tee" fitting & run a hose up under the bed as high as you can get it fastened into place, make a "U" turn loop in the hose, then run that into the canister vent inlet. Aftermarket roll-over valves or vent valves work like the factory ones, except they are on the outside. If you purchase one, place it in the "Tee" hose as high up before the loop. This keeps liquid from going into the canister.

Factory fuel tanks have a bulge or high spot stamped into the tank. The factory fuel pump assembly has the overfill protection device inside, high up on the bottom side of the fuel pumps flange. It has a simple spring loaded float, that pushes against a silicone rubber seal and closes off any liquid fuel from passing.

Using a brake switch to purge gas rich fumes out of the tank, won't work correctly if you think about it. If you are hitting the brakes, you are decelerating. Normally, the PCM shuts of the injectors and no fuel or fumes go into the combustion chamber. This may cause backfire or just raw fuel fumes not burn't because they would run extremely lean...like a misfire.

Just have your programmer disable the EVAP operation, but leave canister purge on. Using the factory solenoid purge valve will work best as it is metered how much it can flow, the internal resistance of the solenoid is check during OBD-II check upon start up and the fumes dumped into the intake, has to be at the front to be equally distributed to all of the cylinders so there is no rich or lean condition in any cylinder.

Hope this helps.