Until we start getting BSPP threaded fittings, I found a way to use 1-¼" NPT threaded fittings on my Cor-20.
I couldn't use the supplied union fitting with hose barbs fittings in my sump. The height of the sump was too short to fit all of the fittings and still have the pump plumbed with flexible tubing. I tried using the pvc conduit fittings suggested on the Neptune Systems forum, but it still wasn't attaching as well as I hoped, so I continued to think of a better solution.
Late at night around 11PM, I had the "Eureka!" moment.
PVC fittings are plastics. Plastics when heated will soften and melt. What is the temperature for softening PVC???
A quick Google search told me that PVC will melt at 250°F. So I heated up the oven and then placed the fittings into a glass dish and let them warm up. I tested the fitting's softness every 2 minutes. I would take the fittings and twist them onto the Cor-20 pump. It was working. The soft fitting was being "rethreaded" by the hard plastic of the pump's volute. After a couple of attempts, I found that if you heat up a sch80 NPT female hose barb fitting for six minutes at 250°, it will soften up enough to be twisted onto the pump with enough turns to create a tight seal. I would let the fitting cool for about a minute and then I would loosen it up and retighten it again. I didn't want the fitting to cool and shrink on the pump without having it remain somewhat loose enough for removal.
I left the cooled fitting on the pump overnight and when I checked on it this morning, it twisted off the pump with no issues. I just needed to test the fitting to see if it was tight enough and had no leaks. And, "Wallah!!" No leaks and it was a perfect fit on the pump.
I'm sure if I were to heat the fitting a little longer (or another time or two) that I could get the fitting to thread onto the pump even more. But for now, it works with no leaks.
I'm not sure what the plumbing experts would say about this quick fix, but it's a simple solution for a perplexing issue.