Just tighten the hose clamps first....
When the reservoir is overfilled (above the "min" level) the fluid will come out, with the engine at operating temps.
There is a small hose specially designed on the lower side of the reservoir, that will dump the overflowing fluid on the ground.
But, if you do have a leaking system, there are special additives to stop it, just ask at your car parts store, they will know what you mean.