Mathematics · Pipes and Cisterns

A pipe, working at full speed, can fill an empty cistern in 1 hour. However, during the first hour it worked at 1 12 of its capacity, during the second hour at 1 9 of its capacity, during the third hour at 1 6 of its usual capacity, during the fourth hour at 1 4 of its usual capacity, and during the fifth hour it was only 1 3 as efficient as it was supposed to be. A second pipe also displayed similar performance, but if it worked at full speed would have filled the empty cistern in 2 hours. Together with a drain pipe that drained water out of the tank at a constant rate, the empty cistern could be filled in 5 hours, all three pipes working concurrently. How many hours will it take the drain pipe to empty the filled cistern if no other pipe was functioning during that time?