Housing
You should try to get as large a cage as possible. Pet rats need room to play and they’ll need room for when they want to be alone. You’ll want to try to get cage that has a plastic bottom instead of a raised wire mesh.
Cage
Rats can easily get their legs caught and injured on the wire mesh when walking and playing. This can result in broken legs.
Aquariums are generally not great for rats due to the lack of ventilation. If you have no other choice but to use an aquarium make sure to get a wire mesh cover so theres at least some air circulation. You may find that you have to clean aquariums more often than cages because ammonia from urine will build up a lot faster in the enclosure.
If you have several rats its a good idea to have a hospital cage. When a rat is sick or injured its important to keep it away from other rats for its own safety as well as the safety of its cage mates. You can make a hospital cage out of any old cage or aquarium you have laying around. I recommend lining the bottom with towels instead of bedding to prevent any dust getting into cuts or wounds that the injured rat may have. You can even put a heating pad under the cage or a hot water battle in the cage if you feel its too chilly. Just be careful that it doesn’t get too hot!
Bedding
Pine and cedar bedding should be avoided. Both give off phenols and acids that are toxic to small animals. Using pine or cedar bedding will greatly increase chances of respiratory and liver problems that can result in death. Unfortunately most pet store employees are clueless about this and will try to push pine and cedar bedding. Don’t listen to them!
I highly recommend Carefresh bedding or something similar. Avoid bedding that looks dusty because it will cause respiratory issues. Also avoid “scented” beddings for the same reason.
Litter Boxes
Yes, rats can be litter trained! Its pretty easy. Most people will use a corner litter tray from a pet store or you could use a small Tupperware container. I recommend using a different bedding for their litter box so that they don’t get confused. I use the unscented version of Yesterday’s News for the litter boxes. I’ve personally never gotten rats to urinate in the litter boxes, but I’ve heard of people having success with that. My rats all do #2 in there.
Litter Box
The best method of training is to wait for them to do their business. Then pick up the waste and put it into the litter box. Pick up the rats and show them where it is. It may take a few days of putting waste into the litter box whenever you see it but eventually they’ll figure out where to go. This will make cleaning the cage a lot easier. If you have issues you may have to move the litter box to wherever you see them dropping their waste. Once you get them going in it you can slowly move it to where you want it to finally be. I recommend having a litter box near where they sleep.