draw a sponge over the slate

In reference to a wet sponge being used to wipe a writing slate clean.

draw a sponge over the slate (third-person singular simple present draws a sponge over the slate, present participle drawing a sponge over the slate, simple past drew a sponge over the slate, past participle drawn a sponge over the slate)

1. (obsolete) Synonym of wipe the slate clean. [19th century]

   Synonym: pass a sponge over the slate