that doesnt look like the kind of gasmask you're supposed to use.. but I see two intake/exhaust holes in the sides, maybe you could rip an intake where the bong is and put another mouthpiece extension on the inside where the exhaust is...
but the way I used mine is, roll a blunt and get someone to blow a huge shotgun into the mouthpiece, and you inhale so much and it fills the mask up, and when you exhale it looks fuckin sweet, with the smoke exiting such a dymanic portal.. its sweet. i dont know about your gasmask though.. different kind then mine.