By definition an overflow tank is not pressurized, so there's only one way in and out. Whatever volume of coolant that regularly moves through the hose, a few teaspoons, is all you get.
A surge tank, OTOH, is more likely to see movement. Still the premise is stupid. Even draining only the radiator (not the block) and getting half the fluid is pretty lazy. That's a better procedure, though, because you're not dealing with potentially cranky block drains. If you insist on not draining the rad look into supplemental coolant additives and a base antifreeze chemistry that supports them. Only really seen on big rigs.