Piezoelectricity in water mediums
You connect the wires to the surfaces of the cylinder that have electrodes, usually made of silver or nickel.  In this case, these should be the inside and outside surfaces.  These electrodes were used to apply the high voltage DC polarizing voltage that makes the ceramic into a piezoceramic.  To operate in water you need to insulate the cylinder since water is too conductive.  You can use urethane if you mix it slowly and wait for most of the bubbles to release.  A few small air bubbles will not significantly affect the operation.  You might want to try RTV rubber compound instead. Be careful when soldering as the ceramic is heat sensitive. First melt a small amount of solder onto the electrode.  Then apply the wire and quickly heat the solder.