When training I was told that a flight starts when the plane first moves under its own power with the intention of flying until it is parked and engine is shut down - ie block time. So taxiing does count as flying time.
However taxiing to the pumps would not count as there is no intention to fly.
On one occasion I taxied out to the hold and then had a problem with my radio, which entailed a lengthy wait before I was cleared to taxi back and park - the whole thing took nearly 30 mins. My instructor told me I could claim this in my logbook as I was intending to fly - however I decided not to bother.