In those days, toilets were called garderobes.

Bathrooms!:
Yes, later on they actually had bathrooms or what they called a garderobe inside the castle. The actual water closets were a wood constructed closet with a hole in the wooden seat. The plumbing consisted of a passage that led down the inside of the castle walls and opened into the castle's sewer system below. The very rich would use strips of linen as toilet paper.... These garderobes might be contained in privy rooms, a separate room near the Lord's quarters that held a large tub for bathing.

http://www.getmedievalonline.com/building.html

... but officials such as the Captain of the Guard had their lodgings in some of the sparsely furnished upper rooms of the Inner Gatehouse - each main living area was en suite with its own "garderobe" or toilet.

http://www.castletown.org.im/heritage/castle_rushen_p3.html

THE GARDEROBES, LATRINE SHAFT & CESS PIT
The garderobes, the mediaeval toilets, were little rooms or areas jutting out from the castle walls. Benches with holes (and sometimes wooden seats) ran along the wall side and human waste would drop straight down a latrine shaft into the castle ditch or cess pit. Guests can see an original garderobe (complete with whiff) in the Kingmaker attraction at Warwick and two others, wonderfully preserved, in the Barbican. It was the job of the gong farmer to regularly clear the ditch, moat and cess pit.

http://www.warwick-castle.co.uk/warwick2004/pr_2005_guide_to...