How would I mount a RO/DI float switch in this tank?

[Gort]

Most of the float switches I've seen like a lever that clamps to a vertical surface. Are there vertical floats?

 

[rhostam]

Most of the float switches I've seen like a lever that clamps to a vertical surface. Are there vertical floats?

I would get an adjustable float valve and invert along the top near the lid. I use two in this manner. RODI direct to fresh water and to saltwater reservoirs. I also use optical sensors to turn off RODI solenoid valve as a second safety.

https://www.bulkreefsupply.com/adjustable-ro-float-valve.html