With experience, you'll learn to notice the "pitch" changes when you flush the toilet shortly before it starts to actually burp. Kind of an early warning that it's getting close. And you'll figure how long you can normally go between dumps. I mark a "T" on the calendar when I dump, so I can pretty much tell at a glance when it might be due again. Just the two of us, but we don't skimp on the water in the bowl, so about every four days I dump and start with about 6 or 7 gallons of water in the tank.
Of course, if you're out in the boonies, running off your fresh water tank, you may need to conserve.