What you claim you want indicates that you don't understand that pipe threads are tapered, and thus only "work" from one direction anyway. The taper is what makes them seal up tight.
ie, a fitting "threaded all the way through" would not accept a fitting in the opposite end. It would have to be threaded from both ends to accept a threaded part in both ends. This would probably be a custom part - buy a pipe tap and modify one (by adding threads to the inside end) is likely your cheapest option, or just have a fitting custom-made by a competent machine shop that directly does what you want.
Re-filling the pipeline - got a lot of brewing to do.