Sluicing

To emit by, or as by, flood gates.

To wet copiously, as by opening a sluice

"to sluice meadows"

To wash with, or in, a stream of water running through a sluice.

(more generally) To wash (down or out).

The act by which something is sluiced; a copious wetting; a drenching.

A kind of ellipsis, introduced by an interrogative, where (usually) everything except the interrogative is elided from the clause, as in "I like him, but I don't know why".