I am running my downspouts to buried pipe to be piped away from my house. The side I am working on has two downspouts. I am also adding about 5 small atrium drains. The underground pipe that will lead to daylight will be about 70 feet long. (This is not a straight run, there are curves as I am going parallel to the front of my house, turning, then going parallel to the side of my house.)

In that 70 feet, there will be approximately 17 inches of drop.

What size/how many underground pipes would you recommend?