You need to have holes in the bottom of whatever you are using if you plan on having them in there longer than just germinating them. You need drainage and to be able to bottom water. What I do is burn a lot of holes with a soldering iron, in straight lines, from the inside of the container so the plastic wisps are touching the soil. Bottom water to field capacity and let drain for a while. Electrical tape over the holes that you made in a straight line, from the outside of the container, sow seeds, and seal. Leave them sit for a few months, gradually punch some holes in the top until you can see the soil dry out, remove the tape, start bottom watering and remove the top. In regards to a fungicide or a microwave, I've never used them for soil. Only H2O2 after the container was opened. I've used a PC on a few batches of soil when I was having problems. The soil mix that I use is pretty simple. The majority of it is MG or Schultz cacti/succulent mix screened through 1/4" screen mixed 1:1 with coir for the bottom. The top 1/4" or so is 100% Schultz or MG cacti soil screened through 1/4" then finally through a fine window screen.