Question
I have a tree in the front yard that has a hole on the trunk where all the
branches go from. It has been there since we moved in 13 years ago. The truck
has water in it about 2-3 ft deep from rain. Should I suck the water out and
what is the best thing to fill the trunk in with or should i just leave it. I don't ant
the tree to fall or rot from the inside. could you email me directly please

Answer
Benefits from filling the cavity are questionable at best. Since the fill material will expand and contract at a different rate than tree wood it can create problems of its own. The strength of a hollow tree comes from the new wood produced after the injury, not from material used to fill a cavity.  

Sometimes the cavity will contain water. The old recommendation was to drill holes below the cavity so the water could drain. However, drilling holes will break the barrier that keeps the decay from invading healthy wood. If water has been present for one or more growing seasons, the tree has already adjusted. You can cover hollow openings with a piece of tin or window screen filled with plaster to keep out animals, water, and to form a surface that allows new tissue to grow over the opening.

When a tree is wounded, it uses its natural defense of compartmentalization to create a barrier between the wound and the rest of the tree. Recent research shows that it is better to leave the cavity open and take the necessary measures required to improve the overall health of the tree. A healthy tree has the strength to compartmentalize and wall-off decay.

I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. this will increase the health of the trees system making it stronger.

The water could be sucked out and then let the hole dry. Cover to keep rain from getting in. Then the hole could be filled with plastic foam. If the hole is too large to fill the entrance could be blocked and then sealed with the foam.

In any case doing this or nothing will both work.