It really depends on how you want your system to be setup. If you want it to be removable or perminent. Its kinda like the algerbra from Junior High - there are mulitpul ways that you can get to the anwser. It just has to make sense to you.
If you want to go the perminent route you should use a quick disconnect fittings from Fly High. You will be able to get bags out easily and make sure that everyhing is good for winterization. That is the way that most wake boat mfg's do it.
If you want I can help you with a layout and a full system. Shoot me an email with what kind of ballast you want and your boat make and model.
We can go from there -
John firstname.lastname@example.org www.waterskis.com