I've bought literally piles of trays from eBay, from 5x7 to 20x24. Some of them are stained, some look new. I've never had a problem with some chemical "contaminating" the plastic and leaking out into my prints. Kind of sounds silly to me, but I'm no chemist. I give them a good scrub with soap and water.
So do you guys just throw trays away every month or something, to prevent this "contamination"?
For the cost of trays on Ebay, seems worth it to me. They're purpose made and have pour spouts. I can't imagine making prints in a heavy pyrex lasagna pan. I'm all for DIY, but some of the sweater box and litter box ideas seem a little extreme, seeing how people are giving stuff away on Craig's list.