As you are going to be moving your lye solution through all three containers(you must add the lye/solid oil mixture to the liquid oils, not the liquid oils to the lye/solid oil mixture), you need to be absolutely sure all containers are safe for the lye to be in. I bought additional containers to be able to do this method. You sell, so you probably already have plenty.
My oils are stored in food-grade plastic containers I get from a restaurant supply store. I've only mixed lye in stainless steel. So my pot for soap making gets the solid oils (where I put on low heat to melt them) and then add the liquid oils. Then the lye/water mix. But now I will try it with putting the solid liquids in the soap pot (as usual) then add the lye/water mix that I made in another stainless pot right after it's mixed to melt the solid oils. Then add the liquid oils.
Selling is something I do very little of. Just want to make that clear. I give away most everything I make. That whole thing got blown out of context on here.