My builder used that black corrigated looking drain pipe to take the gutter water away from my house. However I found that he ran it all into one. Both downspouts go into one and it goes underground across the back of my house and out to the front. I would have prefered that he run each end out to its own side but now I have it across the back of the house and have noticed some moisture. How can I tell if there is a leak without digging it all up? I have poured about six gallons of water in the far side and never saw any go by the other down spout, but do not know how much water it would take to show up on the other side 60 feet away. Does this stuff hold up well? It has been there 6 years. Any help would be appreciated.