If the bowl is already full and you add something, it has to force something out which is actually what you stated earlier. If it's already low and you add something, it raises the WL. If you have bucket of water filled to the brim, doesn't putting your arm into make it overflow? That's what I stated earlier, when I urinate without flushing the WL increases. If agree that if I urinate enough, it fill overflow into the drain but I'm unsure if that's the case. If a Toto's bowl is full to the overflow point that would be more of an issue than my AS Cadet 3.