Number 1 is a fair point. I myself did not know about the radial engines in the middle, or at least didn't observe it, but then again I hardly use the radial engines. And number 2 seems like good info, but your almost always using an engine to empty tanks. The only way you can empty a tank otherwise is by transferring the the fuel out. I was merely trying to answer the guys question and give some basic understanding. He's clearly new judging from his join date, so he's still got a lot to learn yet. Giving him a working knowledge of the game and letting him figure out the specifics through trial and error, the heart of KSP as we all know, is a better way to let him enjoy the game. And if he has another question all he has to do is ask. I don't think anything i said before was inaccurate. Also 2 is not several.