On the 4 inch I'm down to needing to buy the O-rings, decide how to put interchangeable tips on it and glue up. I am using a 1/2 inch "y" valve for the input/drain. We'll have to see how big a pain the valve is to use.
This is where working in a plastics machine shop has advantages. It's likely to be awhile before I will be making 5 lb batches, so the 4 inch not a priority. Some of the work on it will be virtually the same as the 2 inch, 1 1/2 lb version and will be done at the same time.
For the most part the 2 inch will just be a smaller version of the 4 inch. I plan to use the threaded section from a drain and cap coupling and glue them onto the machined end of the pipe, with an inset o-ring and an interchangeable plate with pipe/tube nipples.
The 2 inch will have a major difference in the valve set up. Because of the volume water flow will need to be much more controlled. I am going to use a hose nozzle and if need be a disc with a hole in it, inline to restrict water flow. The design in my head gets a little complicated to describe. This not a run of the mill garage build, therefore I am undecided whether or not I will do a photo post of the build. I'm not here to show off my machine shop/engineering skills or lack there of.