I received my new Tokina 10-17 today and was playing around with the zoom gear and the housing, checking fit and where to put the gear and so on. This will be the first zoom lens I've used in an underwater housing. Though I have owned the sigma 17-70 from day one with my D200 ( it was my first walking around lens, knowing it could be used underwater also). I have never tried it underwater (having used only prime lenses), mostly because there hasn't been a zoom gear I could buy. Most folks who us it underwater use velcro, foam tape or something similar, which I'm told works "fairly" well, but I've never tried it.
After playing with the Tokina 10-17, I pulled out my Sigma 17-70 (non HSM), and to my surprise, the 10-17 zoom gear "almost" fit the 17-70, just very slightly too big. So I simply pull out some black electrical tape, and wrapped it around the zoom ring on the lens, 5 times and the 10-17 zoom gear fit on the 17-70 lens like it was made for it. I thought, this can't be this easy, so I put it in the housing and it works perfectly, like it was made for it,....REALLY! ;D
I know some manufactures (like seatool) don't make a extension\port that works with the Sigma 17-70 but for all who do, (whether it be a Canon, or Nikon mount) a Tokina 10-17 zoom ring, made for your housing, should work with a Sigma 17-70 lens after wrapping the zoom ring on the lens with electrical tape 4-6 times. Personally, this tape will just be left on the 17-70 lens, I see no reason to take it off as functionally everything works, and cosmetically, it is acceptable IMHO.
Just thought I might share this, hoping it may help a few others.