Hi Damien,
Print washing is also carried out in the Jobo drum,with several changes of water depending on RC or fibre paper,discarded water can be drained into a container if you don;t have a plumbed outlet to a drain.
For large prints drum takes about 300ml for each change.
Have almost the same size room and layout as per your sketch in my own darkroom,
so if its of any help you’r more then welcome to visit me anytime and have a look.(i’m in South Dublin).
Would also highly recommend the use of a drum processor in your setup.
I process paper and film using a Jobo CPP2 with lift,which eliminates any need for a sink and running water,also reduces chemical odours to an absolute minimum.
Whichever way you go about it i wish you the best of luck with it,