Note with this flush design: With age the forward (“flush”) jet connection to the upper inlet in the toilet may slowly clog and (over many years) eventually lead to poor, or no flushing action – despite the fact that the main bowl's exit pipe and the toilet's air vent are both open... A test for this is if a “normal flush” evacuation of the bowl occurs when a large amount of water is poured into the bowl at a fast rate. If test is positive, yet the normal full tank flush, in comparison, has diminished flow; or after time no flush, One should check if the flush jet is clogged – leading to the need to snake the jet tube to restart normal flush function... over the alternative to replace the toilet entirely.