Ian,
I'm with Dominic on this!
My DIY cannister has not been to 1m yet (all testing has been in a bucket) but I've been through two sizes of batteries, various o-rings, etc. The toughest part I'm having is getting a good seal for both the light head I'm using, which is an old aluminum maglite, and the cannister.... which I guess is pretty much everything.
However, in my garage at night, it works just great!
To be honest, I just haven't had time to deal with it lately as I've been concentrating on putting together a video housing and camera, but as soon as I get back from this upcoming trip to the Isle of Mull, I'm gonna finish that light. Putting together the electrics was pretty easy, my big problem is finding the right o-ring for my cannister. I'm using a 4" PVC pipe.
Tony