I have a question about Reversible Pump ?
 

With a Reversible Pump do I fill and drain from the same hole in the bag witch would be were the drain hooks up normally? And can I piggyback using my vent line to another sack if this is how I fill the first bags from the drain. I already have a drain for the rear bags.
This is an illustration from wake makers.

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This is what I am trying to acomplish.

Yes, with a reversible pump you usually fill and drain from the same port on the bag (which is typically a bottom port). It is possible to link two bags together off of one pump, but unfortunately I can't quite make out the details in the diagram you attached, so I can't tell you if what you're wanting to do will work or not.

Feel free to contact us and someone can walk through your options on the phone or via email.

I piggy backed additional sacks on top of the hard tanks in my MC. It works flawlessly for the back bags. The front was a littly tricky when going from the one center tank to a bag on each side, but not a problem there either.

Simply put the overflow from the old tank to the bottom port of the new sac, then the overflow from the new sack to the overflow from the old tank.

will this work

That would probably work, but is more than you need to do.

The whole benefit of the jabsco pump is that it can be used for both draining and emptying. You don't need separate mayfair pumps.

Right, but based on his username it looks like he's got a Centurion, and for some strange reason they use a Jabsco just for filling AND sprinkler valves AND aerator pumps for draining. I'm guessing he's just going based off of what the factory installed, thinking they know best (turns out in this case they definitely DO NOT).

Honestly, if you're looking to expand your ballast, I would just replace the factory system. It's such a mess that you'll save money and have a lot easier install that way. We've helped an number of Centurion owners with this upgrade and the difference is night and day.