In the JSON and in the GUI, there should be options to specify the properties for "start manhole" and "end manhole" for Weir, Orifice, and Culvert. So the GUI for these three layers will have two extra tabs ("Start manhole" and "End manhole"), next to the existing tabs "Pipe|Culvert|Weir|Orifice" and "Connection nodes"
There should also be an additional checkbox "Create manholes", similar to the "Create connection nodes" checkbox
In the JSON and in the GUI, there should be options to specify the properties for "start manhole" and "end manhole" for Weir, Orifice, and Culvert. So the GUI for these three layers will have two extra tabs ("Start manhole" and "End manhole"), next to the existing tabs "Pipe|Culvert|Weir|Orifice" and "Connection nodes"
There should also be an additional checkbox "Create manholes", similar to the "Create connection nodes" checkbox