The best product to use as a piston soak is Berryman B-12 Chemtool Fuel Injector Cleaner (part #s 0116 and 0121).  Once you’ve removed the spark plugs, be sure to add enough cleaner to cover the entire piston crown with cleaner.  With inline motors with vertical strokes (like most 4 cylinders and straight/inline 6s), this may only be 2 fl oz of B-12 Chemtool per cylinder, but with V-configured motors (like V6s or V8s), you might need a whole can per cylinder due to the angle of the pistons and diameter of the bore.  If you have a V motor and don’t mind doing this in halves, you can jack up one side of the vehicle in order to flatten out the angle of the pistons.  This might cut the amount of product down quite a bit over the course of the whole job.
 

To perform the soak, remove the spark plugs, add to the COLD combustion chambers enough B-12 Chemtool to cover the entire piston crown and rings, and put the spark plugs back in a couple threads in order to prevent evaporation of the solvents.  The process will benefit from a little agitation, too, so if you can safely rock the vehicle from side to side occasionally, that will improve your results.  Obviously, you’ll want to be careful doing this (or avoid it all together) if the car is on a jack or jack stands.  You can also carefully bubble in a little air either from a compressor or an aerosol duster.
 

Regarding duration, we recommend soaking the pistons for at least 1-2 hours apiece.  However, if leak-down is minimal, you can soak for much longer.  Some users prefer to soak overnight, that’s completely acceptable.
 

Once you’ve decided to end the soak, the cylinder will need to be evacuated of the cleaner/carbon mixture.  You can do this any number of ways including with a vacuum pump or even a turkey baster (which should not be used again in the kitchen).  Note that B-12 Chemtool will damage most automotive paint and clear coats, so be cautious around such finishes.

Thanks for the detailed instructions. On my first attempt, the brake vacuum pump was able to extract some fluid but after awhile, the B12 expanded the rubber seal and it lost vacuum. Other than a turkey baster, may I ask if there are some other methods of extracting the fluid your customers have tried over the years?

Also, if leakdown is minimal (half went down in about 12 hrs on my first attempt) and I can spare a lot of time, can I hand thread the spark plugs to seal up the combustion chamber, drain the engine oil, and rotate the crank so that the fluid is pressured down past the piston rings? The goal of this is to force B12 to clean where it is needed the most - piston rings, piston ring grooves, and piston oil drain holes.

Since B12 caused the rubber gasket on my brake vacuum pump to expand, is there any risk to it damaging O-rings or other engine seals?

Finally, may I ask if B-60 can be used if B-12 for this sticking oil control ring problem? My car is at 128,000 miles. I read that B-60 is for high mileage vehicles and has powerful detergent additives. A mechanic friend highly recommended B-9 chem-dip carburetor cleaner too. Can I use B-9 to get the oil control rings unstuck? Will B-9 damage any engine internal parts?

Thank you for taking time to assist.

Yes, you absolutely can (and should) thread the spark plugs back in a few turns.  If nothing else, this keeps the highly volatile chemical from evaporating.  Turning the engine over by hand is also a great practice but something that some users aren't comfortable with.

As for o-rings, seals, and gaskets, the elastomers used in the engine are usually made out of nitrile/Buna N or neoprene, both of which have excellent chemical resistance.  No need to worry about compatibility there.

As for B-60 versus Chem-Dip, the fuel additive is definitely the safer way to go.  Chem-Dip is a great immersion cleaner, but its water content precludes us from recommending it for use in a functioning engine.  Only parts taken offline should be exposed to Chem-Dip.