|Not strictly a 27 issue, but I thought I'd pass this on as more and more people are wearing these vests.
First, my wife and I took a course on sea survival from Eric Hill, an RCAF navigator aboard RCN helicopters and leader of Canadian Forces' adventure sail training program (http://seasurvival.ca/index.html). Over two days, we learned to handle flares safely, how to board a life raft from the water in full foul weather gear, why you should jump in the water and experience an inflatable vest being triggered in the water and why you should fit leg straps to your vest. Highly recommended if he ever teaches the course near you.
We also learned that the services' support people regularly manually inflate, wash and hang their vests to dry, as a vest that won't inflate, or a vest that inflates and immediately deflates could be very disappointing. We don't do this every time we use them, but we do manually/orally inflate our vests, wash them and hang them up inflated in the basement over winter. That's the easy part.
The less fun part is deflating the vests and re-packing them; getting all the air out so they will pack properly is not easy. I even asked Mustang if they had a means of doing this. No.
But I finally found one this week. 1/4" inside diameter fuel hose, which is approximately 7/16" outside diameter, is a snug fit inside the opening of the oral inflation tube, and effectively depresses the valve inside that tube so that air flows freely out of the vest when you press on the buoyancy tubes. It will also hold this valve open while you gently suck the last bit of air out, which makes it dead easy to re-pack the vest.
Total cost at Canadian Tire for a foot of this miracle solution: $1.19.
If you decide to get your own deflation hose, I suggest you take your vest in and check your store's hose against your vest's tube. My store had clear tube (not fuel hose) that didn't quite fit, while the black rubber hose was a perfect fit, depressing the non-return valve without a struggle.
C&C 27 Mk IV