The trench should be 6" x 6" as stated in the
product label as the large volume of dilution will go deeper than the 6" (the termites usually come closer to the surface to forage as that is where the wood will come into contact with the soil). The drilled holes should be deeper because you are trying to pump in such a large volume of diluted product into a tiny space and the deeper the thin hole the easier it will be for the product to disperse into the soil.