I spoke to Kohler, and they say that their spec is 1/4" slope across the bowl.

Isn't it your tolerance that's more important than the manufacturing tolerance?

I've mentioned before that the big box stores and some internet sites often sell seconds, did you buy this from one of them?

The supply houses most often are selling the first quality stuff. Whatever the source, I'd return it and let them know why.

Toilet purchased from faucetdirect.com = build.com

Call Fergusons, ask what they think about it.

I've purchased "seconds" and reconditioned stuff over the years and in most cases it has been clearly labeled as such. I have an Electrolux vacuum with a "R" melted into the plastic on the bottom of the housing. Back in the days of true "outlet" stores clothing tags would be cut in half or have holes punched in them. Today I think Danner (the boot company) punches holes in the tongue of their boots to signify a second.

I find it hard to believe that Kohler could have enough seconds to supply one Home Depot much less the entire chain. Even then, would be gained by trying to pass off second rate merchandise as first quality? Angry customers? A ruined reputation? It makes no sense.

Now I would buy that Home Depot might be willing to accept lesser tolerances in a particular line in exchange for favorable pricing. Let's say the normal standard is 1/4" but Home Depots says lets create a line called the Flush-O-King 3125 where we'll accept 5/16" tolerance if we can pay you $5 less per toilet.

No company could reasonably product two different quality levels under the same product number. How would anyone tell them apart? The noob on the warehouse floor is issued a UV flashlight and looks for hidden writing on the box?

The whole process of slip casting, drying, firing and glazing is too involved for here. Given all the things involved, 1/4" is doing rather well.

How does the manufacturer tell what's a second? Easy, that's what the QC inspection is all about.

Mike, this has been the case with plumbing fixtures for a long time. Some models of faucets as an example sold by the national chains, some manufacturers would use internal parts of plastic instead of metal. How to tell which from which - where did you buy it? That's easy enough.

Don't take my word for it, ask the next plumbing contractor you run into. That's how I learned about it, and later found it to be true.