TARDIS bathroom

The Doctor's TARDIS had multiple bathrooms. (PROSE: The Bodysnatchers, COMIC: Space in Dimension Relative and Time) At times, companions had their own personal bathrooms near their bedrooms, (PROSE: The Bodysnatchers, The Crooked World) but sometimes the inhabitants of the TARDIS had to share a bathroom. (PROSE: Lungbarrow, COMIC: Space in Dimension Relative and Time)

History
Leela once incorrectly referred to the TARDIS swimming pool as "the bathroom", a habit which the Fourth Doctor temporarily mimicked. (PROSE: Doctor Who and the Invasion of Time)

The fourteenth bathroom had a tap which, by the time the Fourth Doctor was travelling with Romana II, had been dripping for three centuries. The Doctor couldn't find any washers to fix the tap, so he set a temporal containment field around the tap, making it so that every drip was the same drop of water. (PROSE: The Well-Mannered War)

When Chris Parsons explored the TARDIS, he saw a bathroom with with a claw-footed bathtub the size of an Olympic pool. (PROSE: Shada)

When the Fifth Doctor gave Peri Brown a tour of the TARDIS, he pointed out "the fourth bathroom", a room which was opposite "the fifth bedroom". Peri liked the look of the fourth bathroom; it had a deep blue colour scheme and a large bathtub. (PROSE: Doomed)

Frobisher once got the TARDIS to conjure a 3D replica of a Gumblejack in a bathtub. He then pretended to hunt the Gumblejack while having a bath. (AUDIO: The Holy Terror)

Bernice Summerfield asked where the bathroom was when she entered the ship for the first time. The Seventh Doctor pointed to a doorway in the TARDIS control room and told her it was the first left after the zoo. (PROSE: Love and War)

Shortly before the TARDIS arrived at the House of Lungbarrow, Chris Cwej had a long bath in a large, tiled TARDIS bathroom. He fell asleep in the bath and, after getting up, dryied himself with a towel which had been used by Roz Forrester before her death. This bathroom was also used by the Seventh Doctor, who kept a rubber duck by the tub. (PROSE: Lungbarrow)

During Sam Jones' first couple months with the Eighth Doctor, she found the TARDIS bathroom in a different location every morning; she believed that this was the TARDIS playing tricks. On the day the TARDIS landed in 1996 San Francisco, Sam had a bath in a bathroom with a giant brass-legged bathtub. (PROSE: Vampire Science)

However, by the time Sam and the Doctor encountered Zygons in 1894 London, Sam had her own en suite bathroom connected to her bedroom. After rescuing Emmeline and Nathaniel Seers from the Zygons, Sam provided each of them with soap and towels and directed them to bathrooms in the TARDIS. (PROSE: The Bodysnatchers)

Before having dinner with the Doctor on the Cirrandaria, Sam spent some time in her bathroom making herself look nice. (PROSE: Vanderdeken's Children)

After leaving the Crooked World, Fitz Kreiner shaved in his TARDIS bathroom, contemplating the marriage of the Masked Weasel and Angel Falls. (PROSE: The Crooked World)

John Jones used the mirror of a TARDIS washroom whenever he changed his appearance. On one occasion, shortly before the TARDIS received a distress signal from Datastore 8, Alice Obiefune wanted to use the bathroom but couldn't because Jones was in it. (COMIC: Space in Dimension Relative and Time) After Jones left the TARDIS, Alice remarked that she missed his "bathroom-hogging ways". (COMIC: Remembrance)

Bill Potts asked to use the toilet during her first time inside the TARDIS. The Twelfth Doctor gave her the directions from the TARDIS control room to the toilet: "down there, first right, second left, past the Macaroon dispenser". Nardole had used the toilet shortly beforehand and advised Bill to "give it a minute". (TV: The Pilot)