What's the best way to thaw 5 lb frozen chili?

The tupperware nixes using the microwave...

You could place the whole thing in a bowl of very hot water

and keep recycling the water.

As a friend here just suggested, plan ahead :-)

i wanda,soak the tupperware in tepid to warm water just enough to loosen chili, dump into a soup pot with a cup or 2 of water and cook slowly covered so steam and heat jointly thaw chili, scraping thawed chili off the frozen block every few minutes, once you get enough liquid you can just let it cook and melt the remaining lump. sir often so it doesn't burn. slow and low hear.

Hot water

how soon does it need to be liquid again?

Assuming by "best" you mean fastest without burning, and you don't mind investing some work into it. . . Warm the outside of the tupperware in hot water until the chili will come out of the tupperware in one large block. Place the block on a very large cutting board. Heat your heaviest cleaver on the stove (not too hot or it will lose its edge). Use the hot cleaver to cut the block o'chili into smaller blocks to increase its surface to volume ratio. Reheat the cleaver as necessary. BE DARN CAREFUL AS YOU ARE WORKING WITH A DANGEROUS, HEAVY KNIFE AND SLIPPERY CHILISICLES. If necessary, use a mallet to pound the cleaver and drive it through the chili. As you obtain smaller blocks of chili, thaw them in the microwave in a suitable bowl, or place them in ziploc bags and thaw in a bowl full of slowly running hot water. This is a lot of work, be sure you are willing to invest first.

In fact, forget I said this. Find a safer, slower way to do it.

if it has meat in it, you have to heat it quickly to keep it from entering the "danger zone" in which the nastiest of the nasties (bacteria) thrive.