I do a bleach soak for 24 hrs (longer if I get busy and forget about them) followed by 2, 24hr clean water soaks and then I leave them on the back patio (full exposure to sun and rain) for at least a week to make sure any remaining bleach has out-gassed. I probably dont need a week in the full sun and elements...its just what I do.
Katrina, I assume you do that for used pots, right?
Yes, only used clay pots. Because they are porous, I worry I won't be able to rinse all the bleach out so I prefer to leave them in the elements for a period of time before I put an orchid (or any plant) in them.
For used plastic pots, since they are not porous, they get a bleach soak (after scrubbing) and i rinse them well and then they are ready to go.
I should add that I do this in large batches...not single pots. I have a huge utility sink in the laundry room and I am pretty lazy about getting them done so they build up in my dirty pot holding zone... doing large batches makes relatively quick work of the task.