The house I am now in has a GM Delco heat boiler. The bleeders at each radiator are either broken or stripped. I have been trying to release the air at the (I am assuming) fresh water inlet. There is a drain pipe that leads to the sewer. The water is very dirty and seems to let air out. I do this when the pump is running, but not when the boiler is heating. Am I helping to remove some air in the system?