Anybody know anything about running toilets?

[Cary]

The most common cause, as stated, is the flapper. There is a possibility that it's the fill valve or seat, though.

Replace the flapper first. If that doesn't stop it, fill the tank, shut off the water, and let it sit overnight. The water will leak into the bowl and stop (in the tank) at the height of the offending part.

Good luck,

Cary