Process (copied from another forum):
"You want half a tank to 1 gallon of lacquer thinner (paint thinner), try to get a quality one. Can be sourced from local hardware store. This is important to both the health of your engine, and yourself to follow these instructions exactly. You don't want to breathe in the chemicals that are going to be released. You are going to want to drive on a road that will allow you to drive non stop until you get to at least 1/8 to 1/16 a tank. This can be roughly 200 miles. Once you add the lacquer thinner to the tank, go straight to the freeway and drive. You want to do this on a warm engine to start. Your catalytic converter only works once you get to operating temperature, and you don't want deposits to form before it has a chance to burn through them. Once you are on the freeway and at operating temperature, do some spirited pulls. Mostly wanting to get in the high RPM range periodically. This will increase the air flow through the cats, and will also increase the temperature allowing the deposits to come loose easier. Once you get down to either the light coming on, or just shy of it, fill the tank up full. Go jump on the freeway and do a spirited pull or two and you're done.
IMPORTANT:
-1/2 tank to 1 gallon
-pour in at operating temperature
-don't stop driving until you are ready to fill up again
-don't fill up until you have reached at least 1/8 of a tank, preferably less, or closer to the light coming on
-do a couple spirited pulls to get the air flowing and temperature up
-find a quality lacquer thinner with preferably low VOC. (you and others are going to likely breath some of this in, best to keep it as clean as possible, especially for the people behind you)
-Make sure you fill the tank up full once done, and do not let it sit in the tank or the sysytem
-Go for 1-2 more spirited pulls to dilute any amount in the system still.
-get a flexible funnel to pour it in, or transfer it into a gallon fuel container to pour it in.
This process will clean your cat, and any deposits in your combustion chamber, and related parts."
I will go with the rust-oleum lacquer thinner, as it has the lesser % of methanol and listed as low VOC. Will report back!