Autozone sells gumout. So does walmart.but! The autozone bottles are bigger and different labeling,than the smaller bottles,in walmart. Are they different?
You're right- something is going on here, but I suspect it's not with Walmart, oddly enough. My guess is that Autozone and Walmart are both large enough to have their own SKUs for the same product, and Autozone specifically wanted larger bottles to differentiate themselves from Walmart. Sort of a "You get twice as much for one and a half times the cost at Autozone!" kind of deal, but both are labeled for 19-21 gallons.
So either the Autozone stuff is watered down (which I doubt), or you could use half as much as they recommend on the Autozone bottle.