Oil zddp ?

Oil jug? If you don't buy oil in 4 or 5 quart jugs you can always rinse out a gallon milk jug. I have a 6 quart oil measure with a flex spout that works well. Pour in the additive and stir or pour a couple quarts in and then the zddp and add the other 3 quarts. I doubt the cam will go flat or the engine fail if the additive isn't completely mixed right away. No rocket science here.