These guys have it pretty well covered but I just want to
stress to be SURE you get a 120v element. Most at Home Depot
or Lowes are 240v but you can usually find the 120v and a reasonably
priced special socket to fit them.
And you might want to be sure the water pump/supply is off and
there is no pressure in the water system.
I forgot that once myself
I can tell you this, a whole lotta water can come out that hole
in a very little time!
Good Luck!