Adult Nasopharyngeal Swab for COVID-19

NOTE: Recent studies have demonstrated similar sensitivity of nasopharyngeal swabs and mid-nasal swabs for viral specimen collection. So you don't really have to go all the way to the back of the nose. If true nasopharyngeal collection(back of the nose) is specified by the directors of a testing center, patient injury can be avoided with proper technique shown and described here:

Adult Nasopharyngeal Specimen Collection for COVID-19
Upper respiratory viral specimens are taken in the nasopharynx. Not in the nostril or mouth.
Proper Universal Precautions and Droplet Protection PPE are required.
The specimen collection kit consists of viral collection media and a tapered plastic "flocked" nylon swab that is specific for viral specimen collection.

To collect a specimen:
the patient may be seated or standing.
instruct the patient to lower their mask to expose the nose while covering the mouth.
have the patient blow their nose to remove thick secretions that could over the swab.
lift the tip of the nose and introduce the swab into the floor of the nose.
advance the swab along the floor feeling for obstructions and twirling if obstructions are encountered.
Depending on the size of the head, the back wall of the nasopharynx will be encountered when the red mark is between the tip of the nose and the nasal opening.
twirl the swab in the nasopharynx before removing it.
if unusual discomfort is encountered make sure the swab is directed along the floor of the nose and not up into the nasal cavity.
nasal anatomy can vary. The other nostril may be more passable.