No I wouldn’t attempt any cleaning on the inside. We want it so the impurities are pushed by gravity and by capillary action /evaporation to the outside. Just rinse the inside with water. You can use baking soda on the outside – I normally use vinegar or soapnut liquid and a scrubby. The next best thing to do to keep the amphora really fresh is to empty it and give it a sun bath on a baking hot day.