Portaloo

STARDIS had a form of a portaloo and emitted the sound of toilet flushing during materialisation and dematerialisation. (AUDIO: The One Doctor)

The Monk's TARDIS once took the shape of a portaloo. (COMIC: Follow That TARDIS!)

The Seventh Doctor's companion Hex once compared the Doctor's TARDIS to a portaloo, (PROSE: Six Impossible Things Before Breakfast) as did a Dollar Intergalactic employee. (COMIC: Terrorformer)