I'm guessing you mean a dribble running down the back of the pan.
If you bend the stopcock as advised ... you will have no effect on the dribble, as the stopcock is a tap fitted on the mains supply usually fitted fairly close to the floor, under the sink or under the stairs and is used for isolating the mains water supply to a property.
Once again I'm guessing ... but as mosaic says if it is a close coupled cistern The dribble may be caused by one of three things... either the flush valve seal is leaking. Or the inlet valve is leaking and causing the internal overflow to allow a dribble of water into the internal flush pipe, and from there on into the pan.
Or the donut as previously stated, is letting water dribble past it.
Without being able to look inside the cistern it is difficult to identify which of these is causing the fault.
As a rule all dribbles in the pan tend occur when a close coupled cistern is fitted. Unless you are confident in separating water connections and removing a cistern, I feel you should be looking for a plumber.
If you are unsure of how to locate a reputable plumber have a look at your local Trading Standards website. You will find a list of local plumbers who are willing to do smaller jobs.... (jobs under £75.00)
Whatever you do dont bend any metal bar (ball or float vave) upwards as this reduces pressure on any washer and will cause it to leak even more.
Good luck..!