I have a recently installed (2 weeks) toto carrollton that, since installation, has been flushing incompletely and getting progressively worse. Nothing has been dropped into toilet and a large volume of water poured into the bowl goes down relatively easy, though not completely. Called plumber who installed toilet--he removed toilet, replaced gasket, snaked, etc. Flushing is significantly worse now. He is scratching his head, thinks that I should buy a new toilet. This seems to be a reliable toilet, is this plumbing issue really rocket science?