Fill a spray bottle with warm water and several drops of mild liquid dishwashing detergent. The dishwashing detergent will help break down the primer.
Spray the walls with the mixture. Be careful not to spray the outlets or carpet. Let the mixture sit on the primer for several minutes.
Scrape away the primer with a putty knife. Work from the top of the walls to the bottom. Be careful not to use a sharp putty knife, as it may damage the walls. If you cannot remove the primer, soak the walls again with the soap mixture and try again.
Wipe down the walls with a paper towel until they are completely dry.
Lightly sand the walls if primer is still visible.
Spray the walls with water once the primer is completely removed. Wipe the walls down with clean cloths to remove the sawdust.