Back when I was growing up we had gas furnaces and radiators for heating.
Central heating was not common in residential homes back then.
I always remember my parents having to use this key looking thing and drain the radiator into a paper dixie cup. This disgusting sheer black water would come out of the little spout and then the radiator was good to go again with the heating from the gas furnace. I suppose this was the equal of what we have today when we do a central heating and air conditioning system tune up. But back in these days with the gas furnace and the radiator, you had to do it yourself. It was very rare you would ever call a heating and air conditioning company unless your gas furnace would go out on you. The gas furnace actually in my opinion was a little better than central heating of today. The heat was more natural feeling and not to mention, it did not take as much maintenance on the gas furnace to keep it running. The HVAC maintenance that needed to be done was done by the homeowner. No certified heating and air conditioning specialist required! This not only saved lots of money every year compared to today. But it also made things more convenient. You did not have to take off from work or ruin your day just to get an HVAC tune up or check up. You did it all yourself by simply draining the dirty water out of the radiator! I surely miss those days of growing up.