I looked at those a while back, but came to the same conclusion as Citoriplus.

 

I don't know if this only works on carbs and it's kinda redneck engineering and I am sure you will question my IQ, but a friend of mine and I do it this way and there is no mess. Take off the two lines that are connected to the fuel flow selector (where you select on off or reserve). One line is larger and comes from the tank, the other has an elbow where it connects and comes from the carb. Stick the elbow piece into a shop vac, turn on the shop vac and the fuel will begin to flow out of the main line coming from the tank. That is the general idea anyway. This gets out about 98% of the fuel.