Cooling System

When the head gasket went the dealer wanted an extra 120$ to change the coolant. This was the only thing NOT covered by warranty lol. So, lucky for me, my new wife refused to pay that rediculous amount and brought it home for me to chang. I figured it need a good flush since there was the dreaded white goo under the cap indicating oil in the water. Sooooo, my question is.... is there a petcock on the radiator? I looked all over and ended up pulling the lower hose. Also, how much liquid is in the cooling system? Need to know so that I can get a good 50/50 mix. Thx for the help

If you have a 2 gallon antifreeze bottle and pour half of it into a gallon jug then fill it with water. There is your 50/50.

The pet-cock is on the engine side of the radiator on the passenger side.