I like to take baths in my whirlpool tub time-to-time but have noticed tiny particulates in the bath water whether or not the jets were turned on. Barring dirt and grime coming off from me, I've put the blame on the plumbing.
Since I don't use the jets, I've electrically unplugged the pump and decided on a temporary means to plug/unplug the jets. This way I can unplug the jets after the bath to allow the jet plumbing to dry. I didn't expect this design to be water tight. It was basically so that there's no free flow in/out of the plumbing.
To my amazement, I had some difficulty finding plugs out there. So to impress the wife, this design was born.
This is my first Customizer thing and I hope it works for your sizes.
Disclaimer: I take no responsibilities for injury to self or property. :-)
Probably needs support for the o-ring groove. I didn't spend too much effort to perfect overhangs, as the print came out useful enough.
Use with a Harbor Freight P16 (20.6mm OD x 15.8mm ID x 2.4mm Thickness) Nitrile O-Ring.