Anytime you add fluid to a bowl, it will "overfill" the bowl, and the excess will go down the drain.
The back of the trapway is like a dam. The water reaches the top of the dam, and that's the water surface in the bowl.
When you add more water, it goes over the dam and down the drain.
The Drake has a second dam in the lower trapway, same thing happens there.
We are not talking dammed up. The Columbia River has many dams, but there is still water flowing in the river.
So for those that like to add to the river in the night, without flushing to dilute the acid, expect your copper lines to look like the top picture.