I have an XIT404 focus gear set for the Canon 100 EF USM Macro and Aquatica Housing.
The gear set allows manual focus using the housing zoom control.
Included are a 100 EF USM Focus Ring, 100 EF Focus Gear and 100 EF Focus Gear for use with a 1.4 Tele Extender.
This set-up is very user friendly and requires no special focus ports or extensions.
All three for $110, Free shipping within the U.S. Payment by PayPal.
Thanks for looking.