From Bulbapedia, the community-driven Pokémon encyclopedia.
The Digger Drill is a special kind of trap that can be used in the Sinnoh Underground found on the Generation IV games.
When traveling in the Sinnoh Underground, players may occasionally encounter a vendor who will trade certain spheres for items, including the Digger Drill. Most of the time it is a sphere from 10-20. It can be used to create a secret base in the Underground. The Digger Drill is a one-time use item, though more can be bought.
One is also given by the Underground Man in Eterna City as a reward for one of his tasks in the Underground.
Unlike other traps, the Digger Drill cannot be buried.
How to use
To use the Digger Drill, one must walk to and face an area of wall that is wanted to become the entrance for their secret base. Upon using it, the player then loses the Digger Drill, but, as stated above, more can be bought. The player may have no more than one Secret Base. If the player already has a Secret Base, the old one will be removed.