Meaning of backwash

back•wash

1. water thrown backward by the motion of oars, propellers, paddle wheels, etc.
2. the portion of the wash of an aircraft that flows to the rear, usually created by the power plant. Cf. wash (def. 35).
3. a condition, usually undesirable, that continues long after the event which caused it.

1. to affect, as by hitting, rocking, or splashing, with a backwash: a powerful cutter backwashing the skiers.
2. to clean out (a clogged filter) by reversing the flow of fluid: Backwash the swimming pool's filters regularly.