Follow this routine if you have problems with your Hip mobility during squats.
After doing this the first time, I could already notice a difference. After 2 weeks my Buttwink was almost non-existent anymore.
I strongly recommend foam rolling before doing this routine. Try to roll your hip, glutes, hamstrings and quads.
Foam rolling + the routine will take you about 5 - 10 minutes, which will prepare you for your squatting warmup and heavy working sets.
Get strong! Stay healthy!