My advice as always is between uses, after your flushings, brewings, cleanings, is to store the dang thing upside down in your deep freezer. No nasties will grow there. I take it out the morning of brew day to thaw, give it a security flushing, draining and then submerge it in my StarSan bucket until I need it for recirculation ice chilling. Pellet hops in a bag or a hop stopper is a must with these things. Keep the wort going into the Therminator clean and it will serve you many years of happy brewing.
Around every five or ten batches, I have always baked it in my oven at 400 deg for an hour for safe measure.