Hi Brian,
I agree with the other comments already made about using the same fuel line going to the engine and just disconnecting the primer bulb to evacuate all the fuel from the tank. I have a permanent 12 gl tank setup under the cockpit and it took me once about 15 minutes to empty out. I try to maintain the tank full all the time to prevent moisture buildup,, occasionally i'll top off the tank and it helps maintains the fuel fresh and I have not had a problem with my carburetor. However I do go out often about four outings/month so understandably the engine does gets used often and the run time averaging around 2 hours per trip. I feel that adding other permanent fixtures and hardware to remove the fuel would just add potential leaks or failure points in the future. My two cents,,i try to just KISS and not over engineer.
Regards,
Fernando