Did you have a recent head injury, barometric event or bad infection or any ear complaints? Any fever? This could just be watery mucous, but it also be spinal fluid. A rupture of the sinus wall, for whatever reason, could cause a clear yellow liquid to emerge. You need to get this checked out .The common possibilities are allergic rhinitis due to any cause or some cause related to the brain. It is suggested to get a beta 2 Transferrin test on this fluid done. Further testing depends upon the results of test results. Consult an ENT specialist for more details and assistance. I hope it helps.
Take care and regards!