The flowable node class for directional nodes now exists and is hooked up in the code for determining valid neighbours in the flowable node ABM routines.
Pumps have been converted to this as part of the testing.
However, currently only the "raw" registration for this is available, and the pump definition registers it's own callback routines.
Helpers need to be added to flowable_node_registry_install.lua to abstract away the expression of which nodes can flow which ways - valves, flow sensors, spigots and entry panels, for instance, all currently rotate the same way using an upwards facedir, so a helper for these nodes would prevent code duplication.
-- (may not be possible) stop removing water nodes that were not placed by outputs when off
In non-finite mode, spigots and fountainheads will vanish water sources in their output positions, even if those output nodes did not place them there.
This is annoying though not game-breaking in non-finite mode, where water sources can at least be easily replenished.