So you’ve splurged and bought a $20 M15 gas mask, but you don’t want to just take the filter off and risk having fluids dripping into your mouth.
What are you to do? Go spend another $20 bucks on a 40mm Adapter Hose. With this you can extent the air intake away from the front of your face and won’t need to worry about filters. I’d fix the tube against the bottom edge of the mask and use flexible epoxy to keep it in place for a long term finish.