ping

I'm new to the modern style trials bikes but have owned and serviced dirt bikes for over 30years. I recently bought a 2001 TXT and the rear brake felt soft/weak so I drained the lines and put fresh DOT4 fluid in.I've tried to pump, vacumn from the bleader, every trick I know but still get mush.I'm guessing their is a bubble hanging out in the high spot in the line where it enters the front of the swingarm.Sure would like some hints Thanks