I'm guessing you mean NOS (N2O)tanks as in Nitrous Oxide... I don't know anything about them Googled it and this is one of the first links http://www.diy-nitrous.fsnet.co.uk/car-nitrous-system.htm
Im gonna assume you're talking about NOS or nitrous oxide. Its most commonly found in supermarkets as refills for whipped cream cans, supposed to use a balloon to inhale it, i'd never do it, kills too many braincells vs. the high imo. edit: lol cheeba
obviously it's entirley dependent on the size of your tank, the mixtures your burning and how much your putting in your engine. NOS is great business for junk-yards.