Dogdangit! Now that can't be unseen! 
It is a great idea - he is a techy - its obviously a very advanced, approved moustacherator. probably has to pray to it while applying sanctioned lubricants etc to ensure it droops precisely.
used to filter gases,liquids and solids, whilst providing a source of emergency rations in it fibres from previous meals, when needed.
Brilliant idea and all space marines should have one under their helmets as a secondary resperator.. if they don't already.
VEry useful when they get promoted to a higher rank and lose their ranged weapons and helmet, and have to go close quarters/charge everything with their bladed/chainsawed/powered weapon of choice.