I personally have done the "water treatment" and if following the directions, it is done safely and without danger to the motor. I have one of those little camera scopes that fit in the spark plug hole and the before and after was astonishing. Not understanding the process, yes it seems questionable why you would pour water into a motor, but in this case, maybe a question or two would of made someone understand better.

 

This how I do it.

 

seafoam is for pussies

water or ATF can be squirted in with a squirt bottle, so not so much to cause hydraulic lockup, either will break up carbon, check out a head gasket leaked piston, nice and steam cleaned

 

A battery operated mist bottle with a fan works great to get the water to a fine mist, and it works wonders.