Word To Use Today: lavabo.

What's the connection between Psalm 26 and a wash basin?

This:

Word To Use Today: lavabo. This is the ordinary French word for a wash basin, but it is used in English, too, though more often than not (which is still not very often) in the phrases lavabo towel or lavabo basin. 

Dorothy L Sayers used the word lavabo to mean downstairs loo, but that was a while ago.

Lavabo is rather more commonly used to describe the part of the Roman Catholic Mass where the priest washes his hands. In a convent or monastery a lavabo might be a washing trough, but it's the same idea.

And the psalm?

Psalm 26 verse 6 begins (New King James version) I will wash my hands in innocence, and it describes one of the religious rites of the ancient Jewish Temple. In Latin that's Lavabo inter innocentes manus meas... 

Obviously saying the whole line would have been a bit of a mouthful, so people must have decided to stop after lavabo, which means I shall wash.