Perforated pipes are simply pipes with holes in them. The pipes get laid down under the ground and can drain a whole back or side yard. The pipe works in a system and is sort of like a reverse maze. Water from the soggy yard enters any of the pipes under the ground and as water moves through the pipes, it can drain out the holes and eventually run to the lowest pipe and run into the ground. - See more at: http://www.surrey.ca/city-services/3646.aspx#sthash.uHTwzrnr.dpuf