Ive used Bayer brush killer plus they should carry it at most big box stores. . If its a big stump drill a 1/2 hole and fill it up too.

I've used undiluted RoundUp on stumps as large as 3" diameter. Drill a big, deep hole in the stump and just pour the stuff in.

I've painted full strength Round Up on the saw cut and it worked well, too.

I agree to paint full strength Round Up on the saw cut. It also works to cut into the bark all around a standing tree. Paint or spray full strength in the cut. This works even with large trees. I use 37% generic glyphosphate.