Yeah, just plumb it in via the gas block. The only dive, locally, where I've found it necessary that we do locally is on the Hopewell @ ~370fsw. (the props on the Vammen are at 330, but you only scooter through there for a few moments and then come back to deck level at ~300ish where the CMF starts leaking again). It's a very square profile and you're generally only on the wreck for 20-25 minutes. At that depth a little O2 goes a long way so you just plumb in whatever your richest bailout mix is and use that. Don't have to add much.
If the CMF and Solenoid were to fail you'd see it on your HUD/Handset. I've got to say, though, that I've had a remarkably stable experience with the CMF. I almost never have to manually add gas unless I'm working. My unit has been very reliable and bulletproof given how much abuse I've put it through.
