How can catarrh in the eustachian tube be removed?

In general can not: I wonder how you know there is mucus or any pathology in the Eustachian tube. The Eustachian tube runs from the back of the nose (nasopharynx) to the middle ear space. In general this is the result of a viral infection and resolves without any meds. You could try a decongestant for 7 days and an OTC nasal drop for 3 days. In general few, if any doctors would attempt to remove that mucus.