My uncle's homebrew guide says sugar amounts are super easy to mess up.

Did you try using soapy water to find the leak? That's the only way I can ever spot those tiny valve stem cracks lol

Forget the toner, you need to check the building's grounding. Old apartment wiring often has a shared or faulty ground that turns the whole wall into an antenna for your toner signal. That bleed you described is a classic sign. I wasted a whole afternoon once before an old timer told me to test the outlet ground with my meter first. If it's bad, no fancy toner on earth will work right in that mess.