I've reported you to the Sacramento police dept

The rubber wet caps should work fine, the real issue is water leakage into the rubber cups at the membrane seal and also a rather obvious problem, the cost per unit of membrane.

The AM and Milwaukee's are cheap and easy to just screw on.
The plain membrane cost a lot more and you have to DIY it.

Cost is important here as well.

I want the item to marketed and sold, this will make it much more consistent and available and it should not much more than the cost of DO caps, about 8-10$

Milwaukee Replacement Membrane for SM600 Dissolved Oxygen Mete

And no KCL solution but a ref KH solution.

Same type of deal, just made to fit a pH tip is all.

A rubber DIY can be done, I have some new material coming in in a few days.

I think epoxy on a rigid holder would work well for gluing it on. I used an O ring that was very tight. Then slip it down a bit and used a hypo needle to add the KH solution, you ALSO can do the filling before adding the O ring.
This is a bit easier to do and less air bubbles inside.
OSH, Home depot sells all sorts of O rings FYI.

Still, 8$ ain't really saving you much for a DIY pH membrane ref probe adapter don't you think?

Heck, that would not even pay for my time to go buy it and come back.

Very simple upgrade and cheap, pre made for added consistency amongst it's users and availability., Folks can still DIY, mind you, but for saving $ on a DIY project when the item will not cost to start with?

I have some sheets of PTFE membrane coming but have not figured a per unit price for each DIY.
These are the most sensitive to changes in O2/CO2 properties.

Artifical lungs are often studied and they use such membranes to exchange the CO2 and O2. Our lungs are still about 5x as good as the best artifical membrane.

Regards,
Tom Barr