The drain kit allows for a tube and petcock to be remotely mounted, thus allowing the user to drain the can from underneath the car, without removing the can from the bracket. The prefab kit is avail through Mishimoto, though many simply source the component parts from the home or auto store and fad one up themselves for a fraction of the money.
Or, there are people like me who are so cheap, they just remove their headlight, (a simple, quick process), to gain access to the can. This has the added benefit of giving one an enhanced view of the accessory drive side of the engine for purposes of inspection.
I will say I have noted a strong deformation of the O ring after just 3 empties. I will likely replace the O ring next time around with something resistant to degradation and stretching.