There's been a constant drip from the external overflow pipe of my downstairs WC and I suspect a leak inside the cistern itself. I say this because I turned of the supply to the cistern and the water already in it just disappeared. No water leaks onto the floor, it all goes outside. Would you agree that the leak is either a tiny hole in the overflow pipe (the vertical eight inch pipe inside the cistern) or a poor seal betwen it and the bottom of the cistern? If so, how do I remove the pipe - yank it straight up or does it screw in? Any help gratefully received. Thank you.