I think the methane gas produced by your excrements is not a problem . imagine the droppings of animals also produce methane gas imagine an elephant or a horse ... thing to do is try to pollute as little as possible and thus at least you avoid your excrements end up in water such as a river and you make sure you end up being food for other living creatures such as worms and plants and trees because after making your excrements is made ​​to the toilet a little sawdust wood dregs of coffee, a mixture of wood chips .. . that helps your droppings decompose and serve as food for earthworms and plants