Details like the Walthers Cornerstone Industrial Storage Tanks kit will set your factory apart from the rest. The complete set comes with a pair of vertical tanks with connecting piping, a wall-mount tank with regulator/compressor detail, a small horizontal tank with piping (that can be run to the ground or into a building) and a large horizontal storage tank with pedestals. Great for rooftops or alongside a factory building. 
 

Quick and easy detail for factories old or new
Install at ground level or on rooftops for added realism
Parts to build five complete tanks:
Two vertical tanks with piping
Wall-mounted tank with compressor/regulator
Small horizontal tank with piping
Large horizontal tank on pedestals