I've carried what seemed like a 55 gallon drum of fittings around. Literaly one high side compartment filled with them, and we were standardized, except:
The vetrans home that had 4 1/2" hydrants.
The old sections of hydranted area that didn't have Stortz hydrants.
The National Park Service tankers that for reasons I will never understand only had 1 1/2" discharges.
The few 2x 2 1/2 only hydrants left at the research farm.
Relay pumping the above ground water main. (We carried 1500' of 5" on each engine, and had 3.)

You get the idea, and the list goes on. This was a small department.

That's a dry hydrant. Leave one cracked open sometime. Forms a sink hole.

This is a wet hydrant:
[Linked Image from firehydrant.org]

This is not the correct technique:
[Linked Image from sccfd.org]

The correct technique is to get behind the BWM and push it clear with the engine. It can be done. Park infront of a hydrant in Chicago for a demo.