[MBWCC]

The Orvis sinking leader is ~7' long with loops at either end. Assuming you use a loop-to-loop connection between your fly line and your tapered leader all you would do is disconnect your leader from your fly line, make a loop-to-loop connection between the fly line and one end of the sinking leader, and make another loop-to-loop connection between the sinking leader and your tapered leader. Typically a 6-7' tapered leader should be sufficient; whatever you are currently using for a tapered leader is probably good to go with the sinking leader.

Regarding fishing faster & deeper rivers, personally, rather than using a sinking leader or sinking line I would start with a normal tapered leader, maybe go a bit longer if "normal" to you is 6-7', or even add some tippet to the tapered leader you have to up the length a bit, then add some serious weight ~12" above the fly, and simply let the weight put the fly near the bottom. A sinking leader would be my second choice, but only if absolutely needed.