Mark,
I've just noticed that you don't use a reg on your drop tank.
Are you really that hard a diver that you can just sup out of the valve and turn the tank on and off as required?
If you are a bit brassic, if you heat and stretch a sofnolime tub, then chop off the ends you can make a hose. If you then get the cap and drill a hole in it the same size as the hose. Glue the cap onto the stretched tub, connect the other end of the tub hosey thing onto the valve and you have a DIY reg.