Become a sitting tenant (5)
I believe the answer is:
squat
'tenant' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for squat that I've seen before include "house-sit?" , "residence occupied" , "Crouch - occupy a dwelling illegally - short and stocky" , "Short and wide" , "Refuse to move on" .)