Jadnashua
Retired Defense Industry Engineer xxx
The bowl gets refilled at least partly from the hose going into the overflow tube. The path on most toilets into the bowl is through the rim wash ports, so it is quite normal while the tank is refilling for the bowl to refill at the same time. Has nothing to do with the flapper valve.
Many older toilets way overfilled the bowl, so even on an older toilet, throttling the water to the overflow could save some water. Excess water into the bowl just ends up down the drain...unless there's a clog, there's no danger of the bowl overflowing. When adjusting that, add some water to the bowl directly, let it sit to stabilize, note the level, then flush. Adjust the water into the overflow until when the tank is filled, the bowl is just full, too. Some older toilets do not actually need water going to the overflow to fill the bowl, but might clean the bowl a bit better with it...newer toilets try to do all of that with less.
For an older toilet, the most reliable way to reduce water usage is the replace it with a modern one!
Many older toilets way overfilled the bowl, so even on an older toilet, throttling the water to the overflow could save some water. Excess water into the bowl just ends up down the drain...unless there's a clog, there's no danger of the bowl overflowing. When adjusting that, add some water to the bowl directly, let it sit to stabilize, note the level, then flush. Adjust the water into the overflow until when the tank is filled, the bowl is just full, too. Some older toilets do not actually need water going to the overflow to fill the bowl, but might clean the bowl a bit better with it...newer toilets try to do all of that with less.
For an older toilet, the most reliable way to reduce water usage is the replace it with a modern one!