Deep Cleaning Pipe

Clean with pipe cleaners of your choice, you can dip them in whatever spirits you prefer but vodka works well. Just clean it (shank and stem) until the cleaners start coming out totally clean.
No alcohol in the bowl, just scrape or ream it if necessary to keep the cake from getting too thick. Too thick and it might crack the bowl in some cases.
Usually a briar pipe is good to go again after a couple hours.
Unless the pipe develops some sort of bad taste to it, I don't see any point in going further.

Make sure that you clean out the mortise as deposits collect there. To do that, take a pipe cleaner, double it over and double that again over so that you have two thicknesses of pipe cleaner on four sides. Dip that in alcohol on one end and twist it into the mortise and twist it around. To avoid getting any alcohol on the finish, hold the pipe shank side down when inserting the pipe cleaner into the mortise and twisting it around.
You might have to do that twice to get accumulated gunk out of the corners of the mortise. That should take care of any potential sourness. Follow that up with a dry pipe cleaner doubled twice over in the same fashion to soak up any residue.
Also, don't neglect to clean out the airway in your stem and slot. Deposits collect in the slot, so doubling a pipe cleaner or two, dipping one in a bit of alcohol and wiping the walls of the slot, followed by another dry one, will remove any deposits there.
For deep cleaning I prefer to use tapered bristle pipe cleaners to scrub loose any deposits. Fluffies I use for soaking up the deposits.
When you don't smell alcohol in the pipe, the pipe is ready to go, though I usually let it sit for a day.

What both the above posts said.
I'll only add that I wipe a bowl out with a paper towel before it cools. I takes forever to cake, which is how I like it. I ream every 5- 10 years, depending on the pipe.

I'll only add that I wipe a bowl out with a paper towel before it cools. I takes forever to cake, which is how I like it. I ream every 5- 10 years, depending on the pipe.

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That's an excellent way to eventually build a cake that is hard and durable, one that is unspoiled by the tobacco debris that makes for a poor cake.

Ive seen some pretty nasty stuff come out of a pipe using a retort, now I use one for every estate (used) pipe I get along with a good reaming and alcohol wipe in the bowl.

I wouldn't waste good drinking alcohol on cleansing pipes, buy some pure (or as pure as you can find) alcohol and use that. I use 99.9% pure alcohol bought from Amazon and it costs circa £7 per litre delivered.
To use good scotch etc is simply a waste of a good drink and of money. Those who say that using scotch etc improves the flavour of the smoke are talking piffle.
Regards,
Jay.