We will be rolling out several small fixes mid-day today (Jan 29.) We do not anticipate any disruptions or problems, but f you spot any unexpected issues after 12 noon (PST), please report them in the designated thread in the DG Site Updates forum.
Potting soil mix is already sterilized, so there is no need for you to do anything. Lots of folks use either MiracleGro potting soil or Promix because these 2 seem to be of good quality and to give consistently good results. If you were to use soil from your garden, you might want to sterilize it, but it really is best to go with a commercial potting soil. -My understanding is sterilizing soil is a long and VERY stinky process done by cooking the soil in the oven or microwave.
I've had great results without sterilizing either potting mix or containers. My milk jugs are just rinsed well in plain tap water. If I get a stinky one from someone else, I'll use a little bleach water to kill the smell.