I actually need to add a check valve to my condensate drip line/sewer drain connection since it had sewer backup recently (the 3/4" PVC condensate pipe was piped down directly into a 2" black iron sewer pipe). And, I found this that seems easy to install in my setup - however, I would need to install it upside down since in my application the flow drips down, not a pump that pushes up. It says it can install vertically but can it install upside down?
and a link to the instructions: https://images.thdstatic.com/catalog/pdfImages/a0/a034e9df-be8e-40c9-9e58-c800eef33b5e.pdf
and the item at home depot: https://www.homedepot.com/p/2-in-Sewage-Check-Valve-with-Flexible-PVC-Fittings-THD1058/205616018#overlay
and this is where I need to install it:
Can I instead install a drain check valve in the pipe itself? The kind with a float stopper? Should I get a shorter iron pipe and add an air gap?