before draining the stuff out of an engine?

The messy sludge I found in the valvetrain when replacing the valve cover gaskets a few weeks ago was pretty shocking. I've taken some pics and will try to put them up here for you to see soon - anyone easily scared speak up now!

What do engine flush products actually contain anyway? Do you drain all existing oil and fill up with the engine flush or what? Any suggestions are very welcome.

Cheers,

Mas