Aero fuel cap

[Brian foord]

I a planing to put a alloy aero fuel cap in my katana tank. What's the best way to do a breather ? 

[Gammaboy]

breather spigot/hose/one way valve?

[Mr farty]

I use this one on my ET  https://www.newton-equipment.com/tank-vent-valves-small-tank-valve-model-thv45.html    

 

My ET has big holes in the cylinders, big holes in the cylinder head and big holes in the carbs and is run in 36 degree heat and I haven't had any problems at all with it. When it's sitting in the sun there's a constant hiss coming from it  

[agemax]

I am looking at fitting an aircraft type filler cap to an 1100ET tank, any recommendations as to what cap to use? I want a locking cap preferably. TIA