Dean,
Probably talking about the aluminum carb cleaner. It comes in a gallon size pail and you dip the part in supplied basket overnight. I doubt you're get a whole muffler in the pail so you'll have to pour the chemical into a pan. The smell from the chemical is very strong and lingers for many days so use at your own risk.

What does seem to work real well is anti-freeze in a slow cooker. Soak the muffler in the "crock pot" overnight and set it to the "low" temp setting. Be aware of the fumes so place the pot in your garage. Also, use an old "crock pot" for this purpose only.