You know, I rinse and clean all of our milk jugs for recycling. I don't think you can possibly get the "old milk" smell out of them.
Plastic is ok (as mentioned in the post before mine). But glass sure is better in many ways, as it won't hold odors and it's easier to sanitize.
If you can stand to drink Carlo Rossi wine, you could have an unlimited supply of perfect 1 gallon fermenters! They are actually 4 liters, so you can have some headspace for primary, and yet a long neck so you can go with one gallon in secondary. A #6 stopper fits, so an ordinary airlock and stopper can be used. I'd highly recommend trying to do that.