Yes, SIPHON is a Scrabble word!

Letter values in Scrabble US: S 1, I 1, P 3, H 4, O 1, N 1.

Is it a valid word?

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

a tube running from the liquid in a vessel to a lower level outside the vessel so that atmospheric pressure forces the liquid through the tube
a tubular organ in an aquatic animal (especially in mollusks) through which water can be taken in or expelled

convey, draw off, or empty by or as if by a siphon
move a liquid from one container into another by means of a siphon or a siphoning action

Also: siphon off.