How do I Install Fat Sacs?

I'm converting from hard plastic tanks to fat sacs to get more weight and I'm wondering which way to install the new bags. I haven't purchased them yet but from the pictures it looks like they all have two fill openings on the top. Is this the way that you install them or do you face the openings down. It seems like with the openings up you would have a hard time draining them but with them down the air wouldn't bleed out. Also, with two openings how does the overflow work. Does it come out the drain hole and flow through the pump?

permanent or removeable? the holes face up. fill through 1. burp air through the other. if permanent, one hole is to fill and the other needs to have a permanent hose connection to bleed air and overflow so you don't explode the bag. plus what kind of boat? i have hard tanks on my SAN and put removeable fat sacs on top for even more weight.

It's a Malibu Wakesetter VLX. I'm thinking of putting permenant sacs in to replace the stock ballasts which only hold about 300 lbs. each. In the stock tank setup there are 3 hoses. One fill, one drain and one burp/overflow. I guess two is all that you would need if the drain hose will also allow the overflow water to flow through the drain pump when filling. Do you have any trouble with the top mounted drain hose priming the pump when you start to drain?

Mark, I went with Launch Pad sacs in a permanent install. the front sac is rectangular and has a top-fill and bottom-end drain fitting. The V-drive (round) sacs have two holes on one side. I turned it over and fill and drain from the bottom side. My system would not drain from a top mounted fitting. Some of the bag makers will put custom fittings wherever you want them.