Kerbal Space Program

In order to balance more advanced craft (Space shuttles, SSTOs, ... etc) that require a lot of fuel and require the fuel to drain in special ways, it can be very frustrating to get fuel flowing the way you want, and sometimes impossible without placing a structural panel in between parts to keep them from flowing into each other. It would be extremely useful if there was a toggle fuel flow option on tanks, so the only way to drain fuel out of them was through a fuel line. I'm guessing it would be very easy to code back end, and it would definitely make a lot advanced players, veterans, and streamers very happy. :)