Bought a used 2005 Passat V6 with 78k miles on it. Very very poorly maintained and needs a paint job but I think it has a lot of life left in it. Really bad mechanics have been at this car based on the number of missing and broken screws just getting it into radiator service position. Anyway, I just started to dig into changing the timing belt on this pig and when removing the block drain plug, of course, nothing. Pushing a wire on up into the hole is not enough to do anything other than create a very slight super dark ugly brown dribble. There was what appeared to be a mix of red and green antifreeze in the system when I bought the car. I got that straightened out, or so I thought. The color of the coolant in the tank has been normal for the last 20K. Recently restored the heat by back-flushing the heater core with water and replacing the temperature control motor (combo problem). Anyhow, I am going to put the car back together to run the engine (of course, with the newly cleared heater core bypassed) trying a chemical flush called Ironite ThoroFlush. I want to use it with all the old cooling system parts installed so as to not ruin the new cooling system components that are going in with the new timing belt. I read that this stuff is pretty strong but might just actually do the job. I discovered a lot of "cholesterol" in the old hoses too so I am flat out replacing those as well. So, after all that .... The question is ..... Can air and/or water be blown backwards into the block drain to maybe loosen and free up that gunk in there before using the chemical flush without damaging or plugging anything else up? Does anyone understand and know the construction of those coolant flow channels enough to answer this? Thanks a lot.