Plumbing vacuum line as return

I purchased a robot Vacuum last year and my pool was plumbed with a dedicated vacuum line that appears to never have been hooked up. I’m looking to convert it into another return and likely use it for a fountain. While I need to confirm that with a pressure test (shout-out to this site that explained its pretty easy to do) that there’s no issues with the line, I have a couple questions:

1) do I run any concerns with losing too much pressure creating an additional return?
2) how would you...

Plumbing vacuum line as return