Vent tube....
All new batteries come with a new vent line. These lines are used with ATV's and motorcycles. You should not use this.
Your ski came with an independant line that connects to it and vents the fumes outside the hull. You need to find this original line and connect it back to the battery. You do not want any of that acid spilling into your hull while catching air or the vapor condensing on your metal parts of the engine.