Let us know how you get the lines cleaned out. I am doing the brakes right now. I ended up replacing all the lines on the rear end and the soft line. But am afraid to hook up to the mainline until I figure out how to purge. Also need to replace my master cylider and front calipers. Not sure if I have to tear apart the proportioning valve. Did you take apart the proportioning valve or are you just purging?
I had a major plug in the rear soft line that I originally thought to be a bad proportioning valve. So I bought a rebuild kit for the valve from NPD and tore it apart and cleaned it out, there was a lot of grime build up in there.
Once I get the front soft lines off my plan is to disconnect the lines at the proportioning valve and use shop air to blow all the fluid in the hard lines to the front out, I already manually pumped good clean fluid through the rear lines so I know they're good.
The valve is really easy to take down clean and service, so I highly recommend that you do it, just make sure you have a clean work space so that you don't loose any parts. It's cheap insurance and good peace of mind.