User defined conduits can be treated as virtual conduits by setting the Section Type to Virtual. Virtual conduits are not available in the Conduit Catalog.

In the implicit and explicit solvers, the virtual conduits have length but no diameter/rise and span. In these solvers, the virtual conduit must have a control structure (e.g. weir, orifice) assigned to it. If a control structure link is imported from an EPA-SWMM model, a virtual conduit is created with the control structure.

For the GVF solver, virtual conduits can only be used for diversion links. If a control structure is placed on a diversion link, it will be ignored since the diversion is controlled with the diversion rating table or cutoff value.

When switching between the solvers, it is best to set up two physical alternatives when flow splits are involved. The one associated with the implicit or explicit solvers will have a control structure while the one with the GVF solvers with be a diversion link. Both of them can be virtual. It is best to make these links short so that they look like point structures in profiles.