Please tell me if you recognise this flush valve and can tell me what the two screw adjustments do. I guess one adjusts the fill level, but what about the other? The short flush works OK; the long flush does if you hold the button down for a second or so (otherwise it does a short flush) but once it's flushed the water keeps running into the bowl until the button is pushed again. This releases the mechanism so that it returns to the normal position. This only happens when pressing the long flush button - it's fine on a short flush. So any advice would be most welcome!