How do you get hydro pump in Pokemon Platinum?

easy just raise a starter Pokemon like empoleon,swampert,feraligater,or blastoise and if u want ucan hatch an egg and get.Last week i got a lv.100 empoleon and i put it in daycare with a ditto and when the hatched it was a lv.1 piplup and it knew hydro pump!this only works with a lv.100 starter Pokemon