Eliminate charcoal canister + stuff

Well, I see a lot of good reasons to keep the canister. So, some questions pertaining to that.
Is the canister "position dependant"? Does it have to be in an upright position to function? Does it ever reach a "saturation level" and quit functioning? The open bottom breather area is totally crusty. Is there a way to replace the "guts" of a charcoal canister?