Just pass through it, Tora. But the train has to stop at the station So a Piccadilly Line train (which normally runs fat from Hammersmith to Acton Town) would not suffice to tick off Ravenscourt Park, Stamford Brook, Turnham Green and Chiswick Park. Similarly a Metropolitan Line train running non-stop from Finchley Road to Wembley Park would not do to tick off West Hampstead, Kilburn, Willesden Green, Dollis Hill and Neasden.
In fact I attempted the Tube Challenge twice but on the first occasion my friend and I failed. Our last train (to Upminster) was terminated at Dagenham East due to "staffing difficulties". It was the last train of the night and my uncle, who was due to pick us up at about 12.15am (having dropped us off at Chesham at about 5:00am) was left wondering where we were. Thankfully a kindly station bod at Dagenham, to whom I explained our plight (and who was impressed with our achievement), managed to get in touch with his mate at Upminster. He located my uncle and directed him to Dagenham East. No mobiles in those days, of course!