I routed about one inch of my fuel clear fuel transfer line thru the upper
part of my panel. You can see the end of transfering when the bubbles start
going thru the system but you need to be watching to catch the change. The
difference between fuel flowing and no flow is hard to tell by looking at
the line. You can turn the transfer pump off and after a minute or so see
the fuel drain back down towards the pump slowly or switch to the other
tank and note the flow from that tank. The pump vibrates faster when it is
not pumping fuel so my other test is to reach over to it on the copilot
side and feel it's vibration rate. After a little experience you can tell
if it is pumping fuel.

Rusty