Yes I know my car is crazy dirty and needs a paint job. =)
I have a 91 CRX DX. I am not sure if this will work for other years so as far as I know the following will only work on this year / model.
I skipped getting pictures of some of the steps but once you are there doing it it should make perfect sense.
Let's start by removing the rear wiper. You will want to flip up the cover exposing the nut that holds the wiper itself on there, remove it. Pull up and the wiper will be free.
Once you remove the wiper itself there will be a piece of rubber plastic that you have to lift off and expose a large flat nut underneath. You will just need an appropriately sized socket. For now ignore the large flat nut that is exposed, we will remove this later.
Now remove the rear brake light cover by turning the little plastic piece and expose the rear brake light. I don't think that it is necessary to remove the brake light assembly but I did just to get it out of the way and take away any risk of damaging the light assembly. The two bolts hold it in, be sure to disconnect the wire plug.
Remove the plastic garnish that goes around the inside of the rear hatch window so that you expose the underside of the wiper motor assembly. There will be 4 plastic screws to remove, this is a picture of one of them, the rest are identical. This garnish piece fits into a couple of little slots that attach it to the bottom garnish piece, do your best not to break these or the clips holding it on. It may take some wiggling and prying to get it loose.
Now the wiper motor assembly will be exposed. Disconnect the wiring plug. Three bolts hold it in, remove them. In this picture I had already removed 2 of them.
Once these bolts are removed you can then go back to the outside of the hatch and remove the large flat washer. Be sure to hold the motor with one hand while you remove this nut.
Now to fill the hole. There are a couple options that I know of and one that I wasn't interested in involved welding. The other option was to plug it with a rubber grommet. I stole mine from my fire wall behind the right front wheel.
Pop it out and fill up the hole left behind. Stick it into the hole where the wiper was and you are finished. You may want to spread a bit of silicon on the grommet or around the hole to make a better seal.