Dennis, why are you sterilizing it? for seed sprouting or upsizing. I don't sterilize for upsizing. I really don't sterilize per se, just collect the old potting soil in a wheelbarrow and keep it really wet and turn it several times. My best best potting soil for tree pots has been this nasty rancid mix of wood chips and coco hulls I forgot about that I aerated a few times with a pitchfork in the garage while it dried out over a few weeks. There were fruiting bodies all over the place. I let it get pretty dry, reconstituted it and planted. These were honeylocust seeds though. Little seeds might have competition, there was some crabgrass that didn't compost entirely but only a few.
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Unless you are going to reuse soil that had an infection problem (in which case it is best to incinerate it) I have to agree with Tj, there isn't any need to sterilize potting soils.
The exception would be if you are going to use it for growing mushrooms, in that case steam sterilization in an autoclave or pressure cooker would be the way to go.
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