Longbox said it. A petcock for the block drain was common on older models. A hex pipe plug came on newer units.
On the heat riser valve, stuck open isn't a problem, but if you can move it to closed, you can get it free enough to work properly. Squirt penetrating oil on it and work it until it moves freely. If it is stuck, apply penetrating oil and tap it end-to-end, back and forth, until it moves. Then work it by hand until it is free. "Tapping" means firm blows, but not pounding like you want to break everything.
Harvester
