How to prep a #5 plastic container for making yogurt? I made a batch of yogurt that went poorly. I use a Salton yogurt machine which uses a #5 plastic bucket. If this were beer, the recipe would call for baking the container to ensure that all the past microbes are dead. Obviously that won't work for a #5 plastic bucket.

It's already been through a dishwashing machine, so hot water and soap have been covered.

What other means are there for ensuring that the bacteria from the last batch don't show up in the next batch?
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.