Paterson Film Squeegee .

Run this down a wet negative after it comes out of the wash and it removes the water before it can dry into spots.

The blades are soft enough that they won't scratch the film surface. The handle is shaped so you don't apply too much pressure — you're wiping water off, not scrubbing. Pull it through once, hang the film to dry, and you should get clean negatives without water marks.

Worth using with a wetting agent for best results. The two together make a real difference to how clean your negatives come out.