yes,you can do it that way,just be right there looking in the rad..as soon as it sucks it down add more coolant as it gets almost filled and your a little slow adding,the steam and air bubbles come blowing out as your trying to add more cold water..bad,IMO,can cause steam pockets and and hydroshock with cold coolant on very hot cast iron...cracks

yep thats the small bypass hose

LARS is correct running the heater hose with no bypass