What "compulsory formality" was at all camp entrances in chapter 3 of Night?

The "compulsory formality" at the entrance to all the camps were the showers.  Elie, who had been in both Birkenau and Auschwitz in a very short period of time, observed that "even if you were simply passing from one to the other several times a day, you still had to go through the baths every time".

Elie's initial experience with the showers upon entry into Birkenau was much more brutal than that which he endured at Auschwitz.  In Birkenau, after surviving "selection", the newcomers were received by "dozens of prisoners...(with) truncheons in their hands, striking out anywhere, at any one, without reason".  They were ordered to strip, then, shivering with cold, were shorn by barbers in the midst of blows which never ceased to rain down.  They were then forced to run naked to a new barracks, where they were summarily soaked in petrol, which was used as a disinfectant, rushed through a hot shower, then sent into the freezing cold again to another barracks where they were given "trousers, tunic, shirt, and socks".

At Auschwitz, Elie's experience with the baths was comparatively low-key, and he noted, "first impression:  this was better than Birkenau".  The prisoners were seated on the ground before the entrance, and now and then, someone was made to go in the showers.  After being in the hot water, the prisoners waited again, shivering in the night air.  Eventually, they were given new outfits (Chapter 3).