Weeping willows, while beautiful to look at are a menace to the homeowner. The get into your weeping tile and clog it. So I don't need to explain what happens then. And the distance doesn't matter. The roots seek out sources of water. If there is a crack in a sewer or water line, the roots will find it and plug the pipes. If you see a ww tree that grows really fast, its because its found a source of constant water supply. Always a bad sign.