I just found the schematic for the Euronaut, which is one of the largest amateur built submarines
http://www.euronaut.org/page/action/central.php
Look at the detail, it's amazing how much thought went into every single piece of this. Nothing is there by accident and every single section is specifically crafted to be in a particular spot for a reason
Green = Ballast tanks
Red = Trim tanks
Yellow = Fuel tanks
Cyan = Fresh water tank
Peach/Brown = Waste tank
Dark blue = Diver lockout chamber