I looked at the pictures of your 2100 SR. The in-deck ski locker - in between the front seats, drains into the "bilge" so all water from the ski locker will run to the back of the boat and collect under the engine, where the bilge pump will eventually pump it out or when you remove the garboard drain plug. There will not be an actual tube, it's just a hole at the bottom of the back wall of the locker. There will be another hole at the bottom of the front wall in the engine compartment. The water from the locker will drain through the locker hole, flow along the bottom of the hull, and come out the other hole into the engine compartment. Because the holes are not physically connected your snake is probably just hitting the forward engine compartment wall - missing the hole.