transmission cooler flow direction
 

I just brazed a hole in the transmission cooler line on the passenger side of an 85 TD. I want to flush the line before reinstalling, but I don't know if this is the line to the cooler or the return line.
Does anyone know which way the fluid flows on the passenger side transmission line?
Thanks

If the line is off of the car, it should not matter which way to flush the line.

I want to hook it up and let it pump transmission fluid through it, but if I hook up the wrong end it will suck the junk in.
I have already blown the line out with air, maybe I am being too paranoid.