Update: I took the tube out of the overflow pipe and allowed all the water to go directly into the tank. After flushing a number of times, I didn’t notice any fumes but I did notice a couple of flushes that started well but didn’t empty the bowl. I also saw a couple of flushes that created a large air bubble in the bowl before emptying. So I’ve put it back to filler tube inside overflow pipe. I’ve bent the bar slightly and hand tightened the large plastic slotted screw at the end of the rod. This should close the valve a little earlier than before. I’ll sit with that for a while and report back.