I always recommend that you wash your plastic containers out with hot, soapy water. This will ensure that any liquid residue other than water is removed.
You could clean it with a very diluted bleach solution. But I would be cautious doing this, as you need to ensure any traces of bleach are completely gone before using it for gardening purposes.
When you have finished washing them up, then allow the container to air-dry completely after it has been washed and sanitized. For example, I usually leave them for 3 hours or so.
Make sure you remove any labels if you can. I find that hot, soapy water can be very helpful in getting rid of any stubborn labels or glue. I put this waste into the bin and don’t let it go down the plug hole. Otherwise, you might end up with a blocked sink down the line.
Keep the lids if they have one! They might come in handy for some of your other recycling projects.