For many years I flew C/L stunt with unpressurised tanks. I either aimed the vents foward or cut them at a 45 degree angle facing the air flow.

My first experience using pressure was when we started using crankcase pressure in C/L combat.

Should you decide to add a pressure fitting to the muffler I am confident you will be able to do so with no difficulty by the "nut on the inside" method or by tapping the thicker extension part as suggested by Sport Pilot.

jess