727 Not pumping in neutral

I have a 727 that has a Coan reverse manual valve body I put in it a number of years ago. I just put on a bigger pan and remote tranny cooler because it got hot last year. Any way I wanted to flush all the old fluid out of the converter but it has no drain plug. So I ran the pressure line from the tranny to a bucket to start it up and flush it out. For some reason it does not seem to be pumping any fluid when it is in neutral, I know it shouldn't in park but thought it should in neutral. If I put it in 1st it starts pumping right away, drop it back in neutral and it stops. Now I didn't run it through all the gears so is it air or something that is causing this? Or is something worse going on?

None that I've dealt with pump in neutral, it's just the way they are.