Cockatiel has been pooping something that looks and like has the consistency of clear phlegm.

I have a visit with an avian vet in a week, but I'm worried and want to know if I should beg to see them sooner.

He seems totally fine, looks and acts healthy. But I know they hide illness well.

The poop looks exactly like phlegm; it's clear with a bit of cloudyness to it. It also has the same consistency of phlegm. (Sorry it's gross, it's the only way I can describe it). It has a small amount of actual poop in the center.

Has this happened to anyone elses cockatiel? Any advice is appreciated.