If your system is working right any vacuum will draw coolant from the
reservoir tank... that is one of the two main functions of the that tank...
if you keep your reservoir tank full and the system is tight and in working
order...  the cooling system will always be full... on expansion when the
pressure in the system gets to about 14 psi the relief valve in the pressure
tank relieves and puts coolant back into the reservoir tank... that is the
other big job of the reservoir tank...