The only zinc I am aware of is the one on the heat exchanger. It is on the aft lower port side of the exchanger. It is a pencil screw in type monted on a 5/8" plug. The replacement zincs I''ve found are too long and need to be cut down about a 1/2" to fit. Just use a hack saw and shorten it a bit or it won''t allow you to screw in the plug.
I check it every 6 months. It usually lasts about 12 months but don''t count on it.