The tanks were/are used for #2 "Home Heating Oil". in the years before "whole house' heating and {later} air conditioning, e had a tanker truck come to the house and pump it full for the winter. The tank (usually a 55 gal. barrel) had a 1/4' diam. metal tube that ran into the house and gravity-fed a fuel oil furnace. The furnace had a little access door on the front, and you would open a valve cock to let the oil sccumulate into a little pooll in the fire pan at the bottom of the furnace. Then you would light a wad of toilet paper {good wick) and drop it in. As the fire burned the oil - slowly at firs - it woul begin to vaporize the oil as it heated up the combustion chamber, and in no time, the hallway next to the bathroom of your completely UN-insulated three bedroom/two bath concrete block house would be warm. You could not keep any interior doors in the house closed in the winter.