I wouldn't siphon the DSB. If there is anything large sitting on it that you can pick off, ok, but the DSB is not suppose to be disturbed. It develops a bacteria that is anaerobic (lives without oxygen) and it processes Nitrate into nitrogen gas which escapes the tank.
Any macro algae should grow on it's own if it has light (white is OK, a red grow light is better), nitrate and phosphate (which is why you have it in the first place). When it grows and is close to filling it's space, harvest half of it and you'll be removing the nitrate and phosphate it used to grow. If your nitrate and/or phosphate levels are already very low, the cheato may not grow very fast.