A computational approach is presented for steady Dupuit interface flow where the aquifer extends below the sea. A detailed approach is outlined to determine the head at the coastline so that the solution below the leaky seabed may be combined with any type of steady Dupuit interface flow in the aquifer below the land. The method allows for any inland boundary condition including specified head and specified flux; cases of freshwater lenses caused by infiltration are also considered. The approach is implemented in a Python script and a Jupyter Notebook.