N/A Airgun Air tube Maintenance?

soft jaw inserts on a vice .. a small rubber-strap strap wrench, id recommend 'not' actually clamping on a bottle .. also, simply a rubber material type work glove or a piece of rubber type gasket material can make gripping and tightening/loosening things unecessary to actually use tools on, and imo thats what you really want .. most things in airguns 'dont' need to be torqued tight .. endcaps on airtubes etc are held by pressure and the oring, getting them so tight you need tools is unwarranted ..
 
Take a block of wood, and using a pair of dividers scribe the diameter of the bottle or air tube, cut out hole, slice block in half.
On each half take about an additional 1/4” off on the sides with the half circle cuts.

Now you have two blocks each with half rounds to place on bottle, tube, or whatever that’s round that you can now clamp on a vice so both hands are free.