I recently bought an SGE 400 gas mask. It appealed because it has a nice wide visor so you can see the victim’s eyes plus it had three (yes, 3!) NATO 40mm ports which can be blanked off to give you various options. It also has a really easily adjustable head harness to make getting it on the uncompliant much simpler.
I’d hoped that I could have something that was very quick and easy to switch between rebreather mode (air comes in and out the same port) and normal mode (air comes in one of the 40mm ports and out the exhale valve). It’s not the work of a few seconds but the following gives you these options without any destructive changes.
What you will end up with is the external exhale port blocked off, the external front inhale valve removed, and the internal front exhale valve reversed. Removing the valves can be fiddly but a pair of right angled tweezers helps here.
You’ll need to 3D print this STL file and glue a 0.8mm thick piece of scrap latex onto the back of (or two 0.4mm which is the standard catsuit gauge). You can just use superglue, we’re not being precious.
If you would like a much more aesthetically pleasing option, you can print this adapted version from femmyp1xel.