Someone left a big plastic bucket out for garbage collecting. The bucket reads "Paint Latex Primer Undercoater - white" with about an inch of liquid left.

I spilled it out, but there's still the thick remnants on the bucket. Can I just let it dry, cut some drainage holes, fill it with dirt, and use it as a pot? Or do I have to wash it out first? Will the dried paint harm the plant I put in?

"Home Depot sells 5 gal buckets for <$3 good buckets and last a long time,better than food grade plastic which does not hold up to outside sun,freeze ."

Are you saying the white food grade does not hold up as long as those home depot buckets?

Here I thought I was doing a good thing in getting food grade white buckets. I hope they at least last a few years. Thaks for that info, now I will know in the future.

nothing wrong with recycling containers idea. I would stay away from anything that had paint or similar in it. There is always someone disposing of plastic nursery containers, or you can stop at garden centres & ask for free ones - most have drop-off box for people to bring & recycle empties.

I would definitely p/u wooden crates/drawers that are sometimes put out for garbage p/u, as long as they are not falling apart. Just provide drainage holes (drill thru bottom). They will not last forever, but you may get couple of years out of them. You could paint outside if necessary.
Also old ceramic/china bowls, jugs and similar, you just have to provide drainage holes. Doesn't really matter even if they are chipped, it will probably be covered by the plant anyway....just some ideas...