 In fact, if you probably look up French drains, because people are always asking about the size of pipe, do I use 3-inch or 4-inch? Depending on the volume, you may need a 6- to 8-inch. So that would be the only concern that I would have, and don't really have a real formula to tell you how wide that pipe might need to be, because I don't even know how much the existing water...