First of all never leave anything like plastic bags or towels around your pig's cage they will try to eat them.
(Molly got a hold of the hay bag one night and chewed right through it!)
Your piggie needs space to run around. An aquarium is NOT a good idea, because it doesn't give your piggie enough ventilation or room. Your piggie needs a cage with a solid bottom so it doesn't get sores on it's feet.
I recommend aspen bedding. Never use pine or cedar bedding. They have aromatic oils which can give your piggie upper respiratory infections. Cat litter, sand, or gravel would NOT ever work for a guinea pig or other rodents. Towels and fleece are also options but need to be changed EVERY day.
Guinea pigs tend to "go" in one corner of their cages, so if you want to make clean-up easier, you could put a plastic or paper litter box (available at pet supply stores) in that corner of their cage.
Your piggie will need a place to hide and sleep and feel safe. You can purchase one at a pet supply store.
"How much should I clean my pig's cage," you ask? About once a week. But if you have a huge cage with just ONE pig in it you could clean it a little less often.