[Speedslug]

I think K tanks are one of the bigger ones.

I picked up something that was referred to as a "forty" that was about knee high.

I know they make intermediate sizes but it will come down to what ever size you supplier has on hand and how much tank can you 'manhandle' comfortably and safely.

The big tanks are not fun when they get dropped and can cause a whole lot of damage while the gas inside is pushing it around like a balloon if the valve gets broken.

Oh and tanks valves need to be all the opened to the stops or all the way closed, other wise they leak around the valve stem and waste all your gas before you know it.