All these suggestions are great if your aim is to disinfect. That wasn't made clear in the original question.
Or, is the aim to clean and make them look good?
Most clay pots become embedded with (white) calcium deposits that build up as moisture continually evaporates from their surface. Your scrubbing will remove what you can physically get to, with or without the bleach. From a chemical point of view, bleach (which is alkaline) will not remove calcium deposits (also alkaline). Calcium embedded in the pores of clay can be dissolved with a mild acid. I'm not sure what a good mix would be, but given that tap water is already seriously alkaline, I would start with white vinegar (pH 3-3.5) mixed with water at a 1:5 ratio for immediate scrubbing, or 1:30 for an overnight soak - see how that works, and make adjustments if needed. Greene's suggestion to post soak in clean water applies to both basic (bleach) and acid soaking.
