At idle, how long would it take to go through a fuel/water separating filter's worth of fuel? I'm going to put the winterization mixture (2 cycle oil, stabilizer) in the fuel filter but don't want to burn through the oil and into the regular stabilized gas from the tank. Engines are 502 MPIs

Several minutes at idle.

New fuel will still be entering the filter as you run it. Just run it for a minute or two.

I found the easiest thing to do is simply mix the winterization formula in a small tank, connect to the fuel inlet, and run until you start smelling 2-cycle oil. It takes longer than you think, at least several minutes at 1300 rpm or so...

I bought this and it works great. Use the left-overs for winter chain saw work...
http://www.overtons.com/modperl/prod...r=view&i=36861

A typical stock big-block idling at 700rpms is consuming about 1.5 gallons per hour. Not very much, so even that little fuel filter can take several minutes to run.