Laterals are pipes which are connected to a catchbasin at their upstream end, and either a node or another conduit at their downstream end. When connected to a conduit (which is done through a “Tap” node) the crucial aspect is that they do not break that conduit into two separate pieces.

There could be a number of lateral connections to a single trunk conduit. The flows from each lateral are assumed to enter the network at the upstream end of the trunk conduit in the GVF Rational and GVF Convex solvers, and at the Tap node in the SWMM solver. They are not supported in the DW solver.