Definitely an interesting piece. It's great to finally see it up close, so thanks for sharing Andrew! Like @EWilliams, I too seem to recall it having been seen maybe once earlier in the series, though for the life of me I can't recall which episode lol
I think @zredthunder may be correct in that it was made for a scene that ended up getting cut in final editing, hence why it's so difficult for any of us to place it on screen. But like @kertratz said, if anyone can figure it out, it's this group!
Something interesting to note, I actually scratch-built most of one for myself back in the early 2000's, but referred to Sternbach's original sketch for the button placement on the back of the spray head as the only pic available at the time was a downsized auction pic from the front.
Didn't realize the button placement is as you show it, though it would make sense if they simply repurposed an existing Hypospray; they'd just add extra buttons where there was space available.