Being a curious type, the last time I cleaned my intake and the area around the intake and exhaust ports (with the valves closed/got to turn the motor over by hand), I saved the stuff in a bucket, when I was done it was about 1/2-3/4 of a cup of solids. After straining the oil (flushed out of the intake) and spray cleaner, through a paint filter, I got another 1/4 cup of solids or near solid.
Have cleaned out enough pans, to see what builds up on there, often a couple of cups of sludge and some solids. Much less with a synthetic oil. Have scraped most of a cup of sludge off of the inside of a valve cover.
I used to use motor flush on a regular basis (not since changing to synthetic), have seen guys, have to remove the pan, to clean the crap out of the oil pump pick-up, after using a motor flush. Some of the oil passages to the main bearings and lifters, arn´t very large.
Doesn´t seem smart to spray something down the intake and move the crap downstream, all at once, through the pistons and hopefully out of the exhaust or add a can of oil flush that will move gobs of gunk into the pan all at once.