Dip, immerse, submerge, duck, souse, dunk are comparable when meaning to plunge a person or thing into or as if into liquid.
Dip implies a momentary or partial plunging into a liquid or a slight or cursory entrance into a subject.
Immerse implies that the person or thing is covered by the liquid or buried or engrossed in something.
Submerge implies complete and often prolonged immersion (as in an inundation) or a being overwhelmed or, sometimes, overpowered and made helpless.
It may suggest a sinking to the lowest state, grade, or status.
Duck implies a sudden plunging and an almost immediate withdrawal.
Souse adds to duck the suggestion of more prolonged immersion and often of a thorough soaking.
Souse sometimes implies steeping of meat, fish, or other food in a pickle or tart liquid for the sake of preserving and flavoring it. It may often imply not only immersion but a being saturated and, hence, after liquor drinking a becoming intoxicated.
Dunk in its basic use means to dip and soak something (as bread or a doughnut) in coffee, tea, or milk before eating it, but in many contexts it is equivalent to duck or immerse.