The long hose gets routed from your first stage (right post if doubles), down to your right hip where it is hooked under your primary light canister. If you don't have a can light, a holster for a pair of safety shears or similar will work. From there it is run across your chest and over your left shoulder, then around the back of your neck and into your primary second stage.
A bolt snap is tied onto the hose at the fitting screwed into the second stage. This is used to clip off onto your right shoulder D ring when the primary second stage is not in use. Care must be taken to not trap the long hose under anything else. This is verified when you first enter the water.