Hi Martha, while it's certainly not necessary to clean the jar after each feeding (scraping down the sides after a feeding is generally sufficient), when your smaller jar is empty because you're building the quantity in a larger container, I would recommend cleaning it out thoroughly with hot water. The residue on the jar tends to dry up and become rather cement-like, and isn't likely to add anything positive to your starter. A thorough cleaning every now and then will be helpful, but I generally don't use soap, just hot water. 

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