I am in the process of adding a new baseboard heater and I am trying to figure out the proper way to drain my system. I believe I will first need to shut off the valve on the right in the picture below, which should be feeding the zone that I am targeting.
Secondly, I believe that I will need to shut off the return valve for the zone. In the picture below, the three valves on the right all seem to be return lines for that zone. So my first question is, do I need to shut off all three of those return valves? And my next question is where should I hook up the drain hose to? All three of the return lines has a spigot. Can I drain for any of those three, or should there be a main drain line somewhere else? I've added another photo below showing the entire system setup.