Do the eustachian tubes drain in the corner of the mouth near the tonsils? have ringing in one ear, no other symptoms. pharmacist said to take claritin d, will that help?

No, it drains in your nasal cavity. Ear ringing (tinnitus) can happen when you have a blocked eustachian tube so if you have symptoms of rhinitis due to virus or allergy, claritin-D may help. If you do not have any nasal symptoms, claritin-D is less likely effective and you should see an ENT doctor for a thorough evaluation if tinnitus persists.