Vaitupu is reached from Funafuti on the inter-island vessels Manu Folau or Nivaga III. The voyage takes roughly twelve hours one way, less than to the further northern islands. The wharf at Asau is one of the better-developed in the outer atolls, and landings here are generally straightforward.
The schedule is irregular and dependent on weather and demand. Confirm timings with the Ministry of Communications and Transport in Vaiaku before you go, and arrange your stay with a host through Tuvaluan contacts in Funafuti — there is no formal accommodation on the island.