They dont eat or drink. They are kept alive purely by the light. Without it, their bodies go into starvation, and they get weak.
In other words, if nothing is going in, why would anything come out?
They have toilets either in their suits or their ghost does something with it, and if it's the second one I don't want to know what he is doing with it. Unless he is converting it to light poop er... orbs... but if that's the case then when we go super all over things and poop out light we make other guardians clean it up for us....omg....guardians are cats!!!
I've always wondered about the day to day lives of guardians. Is the tower full of squalid apartments that we live in, or do we live in our spaceships? Do we get hungry, maybe barbecue up our countless Fallen victims? Do we subsist entirely on popcorn? Do guardians remove their armor to shower or sleep, or do we even need to sleep? Do we dump in our armor, then just jump off the cliff and have our ghosts ressurrect us free from impurities? What would happen if our guardian got their leg stuck in something and had no heavy to kill ourselves, would we spend millions of years trapped in the same spot?
Their armor includes a Mr. Fusion unit. Turns your "P" into Power with a capital P.
So if you feel nature's call, just...
"Let it go, let it go,
Can't hold it back anymore..."