A typical closed loop has a bulk head with screen which allows water to drain to a pump, that pumps it back into the tank. The returns ususally go over the top of the tank. So there is minimal cleaning. I guess you are referring to people like me, who have their returns buried under sand and rocks. In either case the interior of the tubes stay fairly clean, except for some bacterial slime. the exteriors usually become encrusted with coraline algea. The only things you will have to clean is the pump and the screen. The screen actually requires more maintence than the pump. Thats why I recommed your bulkhead and screen be about a 1/3 way from the top. That way you can hide it with a rock or something yet have easy access to it. I'm using a dolphin 800 for my closed loop on a 75 gallon.
Closed loops are wonderful. you don't have to worry about them over flowing when the power goes out and your tank will look a million times better without all those powerheads in there.