since the muffler is hidden in the cowl of my Hangar-9 P-40 I used a small nylon T fitting,I got it from the local Ace hardware, to make a alternative vent line off the muffler pressure line, when I fill the tank I pull out some of the slack, and pull the plug on the line,placing it in a small cup to catch the fuel.
then when I fill I either hold my finger over the muffler end or I have a little plug that fits the rubber diverter,works great.
the aluminum bracket is drilled so the fuel line slides freely,but the allen head screw wont slip through.