A cage has an enclosure and a waste-treatment tank. The waste-treatment tank has a holding tank and a holder. The holding tank has an internal chamber, multiple vertical partitions, a horizontal partition and multiple filter tubes. The vertical partitions and the horizontal partitions are mounted inside the internal chamber and the horizontal partition is mounted perpendicular to the vertical partitions and forms multiple chambers. The filter tubes are mounted on the horizontal partition. The holder is mounted on the holding tank and has a waste-collection tray with a flushing hole and a trap connected to the flushing hole. Excrement is collected by the waste-collection tray of the holder and divided by the filter tubes to prevent solid waste from flowing directly into a drainage system. Further, the trap is sealed by water and prevents noxious smells from escaping back into the enclosure.