How to prep a #5 plastic container for making yogurt?
For yougurt making, I would say you've covered it.  Someone should correct me if I am wrong, but I would be surprised if anything that would impact the next batch of yogurt survived the dishwasher.

If you want to be certain, though, how about a bleach solution?  Ratios of bleach to water vary widely on the web from 1 tablespoon to 3/4 cup of regular bleach per gallon of water, depending on what you are disinfecting and why. I would think that for this application you could use the lower amounts of bleach.  Soak for a few minutes.  Wash with soap and water.

You referenced beer making:  Beer making suppliers also sell iodine and non-iodine based sanitizers.