Hi Cyclops:

There's loads of info on the bladder system available for you and it is a popular way to control a sub. A Google search will come up with some good links if you look for "RCABS" which stands for Recirculating Compressed Air Ballast System .. which was developed by Dr. Art Broder.

There are many pictures & articles on the following sites and each has a search function to make things easier for you:

http://www.subpirates.com/

http://www.rcgroups.com/forums/forumdisplay.php?f=60

http://www.subcommittee.com/

Hopefully, you'll find this info helpful. Each site has their "resident experts" and assistance is readliy given.

Regards,
Lee Smith