Actually, this is from their website but is referring to cars and mentions putting it through the manifold vacuum line:
To clean carbon and varnish deposits from the tops of cylinders and the backs of intake valves, add 1 oz. Sea Foam to each gallon of fuel. Sea Foam will slowly re-liquefy the varnish and gum deposits that hold carbon together.
To remove carbon and varnish deposits more quickly, Sea Foam can be induced directly into the combustion chamber via the following method. With the engine warmed up and running, SLOWLY POUR 1/3 to ½ can of Sea Foam down the carburetor throat or into any main manifold vacuum line that DISTRIBUTES EVENLY TO ALL CYLINDERS. Note that some newer induction systems, like those found on Vortec and Subaru “H” style engines, do not have any vacuum line that distribute evenly. Consequently, this process should only be attempted by technicians with a comprehensive understanding of the engine’s induction system or use Sea Foam Spray through the throttle body (discribed in a different section of this web site).
Once the product has been applied, turn off the engine and allow the Sea Foam to heat soak for a minimum of 10 minutes. At this time, Sea Foam will dissolve the varnish deposits that hold carbon together. After allowing the Sea Foam to soak, restart the engine in a WELL VENTILATED AREA as exhaust will be extreme for a short time. Drive aggressively for 2 to 5 miles to allow all the atomized carbon to be safely expelled from the system. REPEAT SEA FOAM TREATMENT AS NECESSARY.