Filling Up the Tank
The Glitch do eat. They eat just as we do. Though, unsurprisingly, their process of digestion differs greatly.
When the Glitch eat, food is collected in the body and broken down by bacteria. As the food ferments, methane gas is released and collected.
The methane is then burnt, and the heat created used to power a gas turbine. As such, each Glitch has his or her own internal combustion engine.
Of course, not every scrap of food breaks down, but what's left makes a very fine compost. These leftovers are... 'expelled' from the body.