where to run vent line on ballast system

I've seen a couple different diagrams through a search i did, and still not sure if i've got a 100% answer. where do you fellers that have done your own ballast system run your vent. do you tee it into your drain line(i've got the pro x series 750 pd sacs from fly high) or do you run a separate line out the side of the boat?? any help would be greatly appreciated. I've got everything in place already, and just need to get the ballast switcher from the stealer, and cut holes in the side of my boat for the drain ports to empty the sacs. thanx ryan