Block Drain, Got lazy, Now have Question
 

I just completed a citric flush on my 75 300d OM617 (w115 car) and flushed and backflushed many times and also used air to blow out remaining water. Yesterday, I noticed when bleeding the system that I thought I detected a rush of rust colored water and wondered since I did not open block drain is it possible to trap rusty water somehow in spite of flushing/backflushing? I must have flushed about a dozen times until water ran clear. Someway that water can be trapped in the circuit near the block drain? Thanks!

"Trapped" probably isn't an accurate description. It's more like "not inclined to flow up hill."

Don't be lazy; pull the plug.

Heater matrix?

That makes sense, solids sitting low - betcha a bunch crap is about to leave the block drain, last time I do that! Thanks!

Service manual says to only do the citric acid flush after the system has been deoiled whether there is any indication of oil in the system or not.

yep, did that with Shout as before -