Is my toilet operating properly
The overflow tube empties into the bowl. When the bowl water level rises to  certain point, water starts going down the drain. You can verify this by pushing your float down in a full tank. You'll notice that the level in the tank rises but the level in the bowl rises too. You can see water entering the bowl usually from the rim. Water can only get to the drain by going into the bowl first.
(Picture from Home Tips)