Because that's where the gas goes, lol. And so you know how to put it back together without messing up. Once you have the baseplate off, there SHOULD be an O ring around the bottom of the reservoir, take that off and soak it in silicone oil over night, once you've done that, put it all back together, fill it up with gas and it should work. If you're going to store gas magazines you need to leave a bit of gas so they don't dry out.