While tympanostomy tubes are not common in adults they are not really all that unusual and it really is not anything that should require a dive ENT to answer. A call to DAN may be helpful as well as the linked article by DocVikingo. Even the ENT that placed the tubes should be able to give him appropriate advice. While prehaps not specific to diving, they deal with tubes and swimming routinely. And prehaps our resident diving ENT doctormike might post.