I soak mine in a 10% chlorine bleach and water solution for about 10 min. L.B. This brings up an interesting point - I was going to start seeds last night, but then I recalled that I had read somewhere that one should always use impeccably clean trays for seed starting. I checked the back of the seed mix bag and it said the same thing. So, I soaked my old trays, lids, and six-packs in hot, soapy water and the rinsed them off. Of course, they are cleaner, but not "clean". The whole time I was wondering, "Do I really need to be going to all of this trouble?" What has been the experience of the list? Do you re-use seed trays, etc.? I can replace my setup for about $4 per 72 plants ( would only need three sets) - should I do this? Or, am I just making more work for myself? Thanks. Matt