(Chem.) To clean (a filter, a chromatography column, a water softener, etc.) by passing liquid through in the reverse of the normal direction of flow. This procedure dislodges particles which clog the pores of the filter or column packing, removing them from the filter or column.
... still—and still not without its qualities. Here's one at least who finds it the very salve for weariness. Playing it, I often feel in the trance of rapture. I wish to God I could live my life upon the flute, for there I'm on the best and cleanest terms with myself, and no backwash of penitence. Eh! listen ... — Doom Castle • Neil Munro
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