This may seem a bit long-winded, but here are a couple tips I can throw your way. I've restored a few old that were very dirty, including one that had so much cake you couldn't fit a pencil into the bowl. I kind of like the challenge.
Obviously, get the stem off first. If it's oxidized vulcanite I scrub it out with alcohol first, then cover any makers marks with vaseline and throw it into a jar of bleach for about a day. It works well, but you spend some time sanding it smooth again, particularly if its low quality vulcanite. If it has any metal like a stinger or a screw in tenon, oxy clean may be a better way to go because bleach will corrode metal. I haven't tried oxyclean myself yet
For really thick cake I start with the smallest reamer I have and work up in size until you get the cake down to a thin layer. If it smells really bad you may even want to sand the bowl almost down to bare wood, but that can be tricky and you may need to break the pipe in all over again.
A drill bit of the appropriate size for the draft hole works well to ream the big gunk out. Then I go at it with everclear and a shank brush. Once I get the worst of the gunk out that way, I switch to alcohol and bristle cleaners until they come out clean. That can take some time.
Cleaning the outside of the bowl can be tricky as well. If it's really dirty and the old spit and scrub isn't getting me anywhere, I go to 0000 steel wool to get the dirt off and see what lies beneath. Sometimes you'll spot a crack or nasty fill that was covered by grime. On a few pipes I've actually sanded the bowls down to bare wood, starting with 400 grit and going down to 1500 and the 0000 steel wool. Again, that can be tricky because its easy to sand off any brands on the shank. If you do go that far, look for good quality leather dye to re-stain them. It's alcohol based and you can find a number of colors and shades of brown.
From there I move on to the the sea salt and alcohol (or cottonball and alcohol)treatment for at least a day. If you have gone so far as to sand it down, you'll want to do this before staining, as spilled alcohol can remove or stain the dye.
Then it's all polishing and waxing.
Unfortunately I don't have before picture, but this is the one I mentioned that was so caked up. It was also black with years of dirt, so I did take this one down to naked briar.
By the way, if anyone knows who made pipes for Texaco, I'd like to know. It's great old pipe.
Yeah, this was long-winded, but I hope you found it helpful and not to much of a redundant information.