Alien Director's cut - What does Ash drink in the movie?

Here is a nice interview with a large portion of the original filmmakers, in which they discuss how Ash is drinking milk.

From what I can ascertain, the androids in this film series can indeed drink fluids - but in this case it seems to be a precursor for a later gag in which Ash sweats a white fluid in an approximation of an 'android orgasm'.

From an interview with Ridley Scott:

Interviewer: Just before assaulting Ripley, the robot starts to sweat....

Ridley Scott: This is one of the humorous touches in the film. At the end of the previous scene, you've seen it drink milk, or some liquid with which it feeds its circuits. The drop that appears on its forehead is an alarm signal, a way of warning the audience that something is going wrong
.... and I always thought that it was interesting that er, do humanoids have sexual urges, what would be nice is that this is the closest he gets to sexual relationhsips (smirk)

(Shepperton Studios 1978 documentary (The Making of Alien ) )