Building a covered pit filled with gravel or loose stone, into which drainage from roofs, areaways, etc. is piped to seep into the surrounding soil
See dry well in American Heritage Dictionary 4
also dry·well(drīˈwĕlˌ)
noun
A subterranean chamber near a building, having stones or gravel inside and used to collect rainwater runoff from the roof of the building as a means of avoiding soil erosion.