Drain punch is for steel types that threatens to wall Garbodor such as Orthworm Iron defense.
While Gunk shot is for Grass/Fairy such as Primarina, Clefable, etc.
Seed bomb is for Ground that threatens Garbodor such as Landorus-T, Excadrill, Charizard X
And Rock blast is to make sure sash mons are dead while killing Others such as Blaziken, Ribombee, etc.
(While using Weakness Policy is risky it'll be worth it once it gets hit by a ground/psychic [atleast lives 2 depends])