What are the consequences if you screw up...? Sounds like youd have to screw up on purpose to do anything wrong.. but im just curious..?
Hydrolock. Although I've never heard of anyone actually having this happen.
Just make sure you don't let the booster tube suck the Seafoam in all at once. Pour 1/3 of the can into a seperate container, put your thumb over the hose and let it off enough so the hose sucks the Seafoam in SLOWLY. Do that and you'll be fine.