I decided to try to bleed my pump last night (Myson SD53). I took the little plastic cap off the central nut and tentatively unscrewed it.... I've never tried bleeding the pump before and I expected great floods of water at any second. I unscrewed the nut until it pulled loose and yet only a drop of water at most came out. Is this the correct nut to be undoing to bleed the pump? The pump has a label saying "if pump sticks unscrew central knob, pull to locate in shaft and rotate". It doesn't mention bleeding.