Catheter bag problems

My brother is gonna be home with a catheter and squeezed his bag enough that it had that vacuumed look like when you squeeze all the air out of a ziplock bag? And now (1 minute later) he's worried that it's not draining properly because there is a bit of urine in the catheter. Ideas or solutions, etc? I'm still a student so there's still a lot I don't know...
We are unable to give medical advice per the Terms of Service. Please seek the advice of his physician. Thread closed.