Oakum
Oakum can be used to seal cast iron pipe drains. After setting the pipes together, workers pack oakum into the joints, then pour molten lead into the joint to create a permanent seal. The oakum swells and seals the joint, the "tar" in the oakum prevents rot, and the lead keeps the joint physically tight.
Today, modern methods, such as rubber seals (for example, gaskets or o-rings) are more common.
Zakynthos
The importance of this alliance for Athens was that it provided them with a source of tar. Tar is a more effective protector of ship planking than pitch (which is made from pine trees). The Athenian trireme fleet needed protection from rot, decay and the teredo, so this new source of tar was valuable to them. The tar was dredged up from the bottom of a lake (now known as Lake Keri) using leafy myrtle branches tied to the ends of poles. It was then collected in pots and could be carried to the beach and swabbed directly onto ship hulls. Alternatively, the tar could be shipped to the Athenian naval yard at the Piraeus for storage.