Seafoam directions say to try to use the PCV line or brake booster line. Around here Advance Discount Auto parts is supposed to have it. I think you use 1/3-1/2 pint for injestion and pour the rest in the fuel tank. They say you can put it in the oil too, but I don't think I'd try it, myself.
Seafoam is to clean soft carbon off of valves and hard carbon off the tops of pistons. Word of warning, when you restart it after letting it sit like the directions state, your car probably will smoke like you just blew it up, for a few minutes. I haven't used this stuff yet, but I've read a number of good reviews from people on CrownVic.net.
General Motors makes a similar product called Top Engine Cleaner. It's used similarly, but contains water along with the cleaners. Seafoam is all petroleum products. Some guys let the car injest enough Seafoam to stall the engine, I don't think that's it's intended use though.