The typical technique is to run the line in question until you smell chlorine at the faucet. So, just turn on the hot water at each fixture (one at a time) and wait for the odor. When you can smell chlorine at all outlets, you are done.
Formerly: 2005 Airstream Interstate (Sprinter 2500 T1N)
Now!: 2014 Great West Vans Legend SE (Sprinter 3500 NCV3 I4)