A conduit for dispersing or gathering liquids in the earth has an arch shape cross section and alternating peak and valley corrugations along its length. At one end of the conduit is a sub-arch for receiving a pipe. In one embodiment there is a discontinuous valley by the sub-arch and a continuous web on the peak corrugation near the sub-arch in combination with cantilevered legs. In another embodiment the web is discontinuous while the valley is continuous in the region of the sub-arch. Both essential constructions provide a strong joint when conduits are mated to each other and are buried in the earth and subjected to a load.