We have an American Standard Cadete III toilet that needs to be flushed twice in order to clean out waste.?

I called American Standard and was told we needed a flush valve and this would correct the problem. A friend had the same problem and was told it was a casting problem. His toilet was under warranty. We don't use this toilet all the time and didn't try to correct the problem, thus the toilet is not under warranty. Has anyone else had this problem and if so how did you fix it?