Rat cannot be kept in tanks, due to the lack of ventilation. Tanks also do allow good climbing or enrichment opportunities, risking both a bored, unhealthy rat and and overweight one.
A large, barred cage is ideal. Something live a Savic Freddy 2 or Ferplast Jenny is good for pairs or small groups respectively with larger cages such as the Explorer, Savic Royale and Furet Tower housing up to 12. The fancy rats cage calculator under Further Reading can calculate how many your cage can hold. A good rule is to allow 2 cubic feet per rat, with a minimum cage size for a pair being 80x50x50cm.
All mesh floors should be avoided or covered since like Degus this could cause your rats to develop a condition known as bumblefoot.
Rats are prone to respiratory ailments and should never be kept on sawdust, wood based cat litter or anything pine or cedar based. Good substrates include Aubiose, Bedexcel, Finacard or shredded paper. Megazorb and carefresh can be used, although some keepers have reported problems with this so this should be carefully monitored.
Rats are very intelligent pets and do need a great deal of enrichment and entertainment. They can be trained to perform simple tricks and may respond to their name. Good toys include large wheels, hammocks, nesting areas and igloos, rope toys as well as more natural enrichment such as 'pea-fishing'. Pea-fishing involves putting some frozen peas into a bowl of water and letting your rats fish them out. This is particularly useful for the summer months as Rats regulate their body temperature through their tails and can use the water to dip their tails in to cool down. For other enrichment ideas, see our article on rodent enrichment.