You can use Seafoam either of the ways you mentioned, but it will do different things. To clean gunk out of your crankcase, pour some in with the oil and ride the bike for a couple hundred miles. To clean out the entire fuel system, pour it into your tank. This will also take light varnish and gunk out of your carbs and off the valves. To really clean out the carbs, combustion chamber and valves, feed it through a vacuum line or directly into the carbs. Also, most people don't know this, but Seafoam also comes in an aerosol can and is labeled as Seaform Deep Creep. It's the exact same formula, but just aerosolized. I've used that by spraying it into the carbs with the motor running.

 

im gonna have to try some of that "seafoam deep creep", im pretty sure that i would **** up taking my bike apart, so an aerosol would be great. also noticed that there were 2 other illinois f3 owners that posted here!