To boondock or not?

Good source of information about what's possible (in the US) is the local US Forestry district office. They can tell you the LOCAL rules about NFS camping. Rules very by forest district and sometimes by seasonal issues so it's always best to check in. With a little practice a couple of people should be able to camp for at least a week on a 30 gallon gray tank. Economies are generally found in HABITS much more than equipment. In SOME areas (again, ask) it is permissible do dispose of gray water and sometimes even galley water in the forest. Where this is allowed the black tank become the limiting factor along with the fresh water capacity (which can easily be supplemented by any number of means). I've never seen boondocking as an economy issue however because it's hard to put a price on enjoyment. If you enjoy camping in a crowded rule enclosed commercial camping space (I avoid calling them campgrounds) then that's fine but if you enjoy being out in nature and experiencing great scenery and peacefulness then you have to prepare for the adventure.
Good luck / Skip