It leaks a lot less than the drain hole in the muffler does. This type of throttle body does not even have a minimum air flow screw so it will go all the way shut. My last one had a screw so I just backed if off till the blade closed all the way. Neither one leaks enough to hear at all. I was concerned about burning the aluminum body or the bushings up but driving all last year even with a lot of nitrous passes didn't hurt the original one at all.