Your coolant system doesn't suck coolant in from the overflow tank when it's running warm or hot. It will expel coolant to the overflow tank because of the building pressure heat causes.
Then when your bike cools back down after you're done riding, it sucks the coolant back into the radiator. As the temp lowers, pressure is relieved, and as it gets cooler, a slight vacuum is created, which is why it then sucks coolant back into the rad.
Unless your rad cap is bad. Or your hose is leaky, pinched ,clogged, etc. It's a good idea to thoroughly clean your overflow bottle too.