I do not know if your Hunter 26 was on the trailer or in slings of a boat hoist but I will tell you and anyone to let the water out or you will damage the hull, seal of the tank lid and possibly the trailer. Always open up and drain the water out when out of the water. NO IFS ANDS OR BUTTS! I have seen too much damage from that as a former dealer heavily involved with that boat
As for the water, it is 2000 pounds trying to escape out when the boat was lifted out of the water. Yes, you probably will not have a good seal with that much weight trying to get out. As for the seal, when sailing, it keeps the water from draining when heeled but remember that the water is not that heavy like the above incident. You can take the seal off and either replace it or leave it alone.
