Jet Tub Plug Set

My in-laws have a jet tub and only use the jets about once a year so they were looking for a way to plug the various jets and intakes so that when the tub gets used, water doesn't end up in the pipes to sit there and stagnate and get mouldy. Unfortunately, they couldn't remember the name of the manufacturer (the tub is about 30 years old), and using something like rubber stoppers was out of the question.

I was playing with Fusion 360 and had just figured out how to make a thread so I thought I'