2001 Cadillac STS Installing the freeze plug

The step-by-step guide is basically "pound the old one out and pound the new one in". You can get a complete set of core plugs, (aka freeze plugs), for your specific engine at any auto parts store, or they can look up the size you need and sell you just one. Many parts stores now borrow or rent tools and they will have a kit for installing the new plug. It's just a pair of extension handles and a variety of discs. You pick the disc that matches your plug, and use the handle that gives the best access.

Clean the hole out first of any rust or scale. I like to add a little bead of gasket sealer around the new plug but I doubt that helps much. It's not necessary. If you have a straight shot at the hole you might get the new plug in with a socket that just matches the diameter of the lip. Don't insert it too deeply, and don't hit it in the center. That will deform it and shrink it causing it to leak.

Usually core plugs corrode through and don't completely fall out. You might look if there was a block heater in there. It will be hanging nearby by the cord. Sometimes the wing nut that holds them in breaks but the heater won't push out until the system builds pressure.

You can also buy rubber core plugs that tighten down with a wing nut. Those are nice for places you can't reach without removing a lot of other stuff.

Nope. They're all different. Welcome to our world. Some are real easy to get to because they're right out in the open. Some require the transmission to be removed. You can't get much more difficult than that.

The closest thing to what you want is the manufacturer's service manual but even that won't give you a step-by-step procedure. They only show the engine block after everything has been removed. YOU are actually in a better position to know what to do than the rest of us because you had it apart already. The best I can suggest is if you can slip your hand in there to sneak in a rubber plug, that might be a better option. Some of them have a hex nut to tighten them that you can reach with a wrench.

I'm confused. The tail pipe and coolant reservoir are miles apart. Are you seeing leaking coolant or are you hearing and exhaust leak?

Water inside the tail pipe or dripping from it is normal. That is a byproduct of a properly working catalytic converter.

Another way to find a leak is to drain all the coolant from the reservoir, (if that's what you suspect), then inject a white, non-toxic smoke from a smoke machine. You might find one of these at an auto parts store that borrows or rents tools. Stick the hose in the reservoir through the cap, and seal it with a rag. The smoke will be under two pounds of pressure and will sneak out any leak so you can see it.

For the engine information you're looking for nothing beats a paper service manual from the manufacturer. You can order one through your local dealer or you may find one on eBay. You can also buy a subscription through one of the online services. There are links on this site to "Mitchell On Demand". "All Data" is another one. DVDs and online services are very miserable for finding stuff in a hurry but you'll get the same stuff that's in the original service manual, plus you'll find listings for related recalls and service bulletins.