I just took a trip to Home Depot. While I'm not 100% sure I got the right parts, I did manage to find something with the label "polybutylene sharkbite adaptor". In the photo below, it's the piece on the right with the grey part sticking out. Seemed the right size, right name, etc.
And, they had a male pex shark bite to screw into the filter!
I picked up a 10 foot length of pex and I believe that's all I need to re-assemble!
Thanks for pointing me in the right direction, Eric!
Originally Posted by eric1514
That gray pipe, I believe is polybutylene. It's no longer used. There are sharkbite fittings that can adapt that stuff to more common pex tubing.
I would assemble what I needed in pex and then adapt that to the existing old polybutylene with the proper sharkbite adaptors after cutting off those old threaded connectors.