720 gas fuel delivery system question.

I had the same trouble with my 720. That darn fiber based gasket that goes under that bowl that you're talking about is the problem. Getting it lose can be a bit interesting. Once you get the sediment bowl assembly off from the little metal "bowl" then you can screw off the cap on top of it. In this case it should have a line attatched to it with a swivel on the gas tank end. Once that top cover with the hose attatched is off, then you have to find a thin wall socket. There is a bolt in the bottom of the bowl that you have to get lose. This can be a bit challenging but it is possible. When you get this lose then you can find the gasket at the bottom. I have had great success using a soft copper washer in place of the "factory fiber" washer. Once you get this done you should be set. As to the function of the bowl, it is just listed as the body of the carburetor inlet. Good luck and post back with any questions. I'm no expert on old tractors, but I've done this very same procedure more than once (not anymore thanks to some good advice of an old JD mechanic with the soft copper washer).
Tyler-MO