Yes, LAVATORY is a Scrabble word!

Letter values in Scrabble US: L 1, A 1, V 4, A 1, T 1, O 1, R 1, Y 4.

Is it a valid word?

LAVATORY is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a room or building equipped with one or more toilets
a bathroom sink that is permanently installed and connected to a water supply and drainpipe; where you can wash your hands and face
a toilet that is cleaned of waste by the flow of water through it

Also: flush toilet.