Ignore that guy, he's pretending to be ignorant.
And don't mean to be pedantic, but the gas didn't come out of the shower heads at Auschwitz. They dropped the gas capsules through ducts in the roof, according to Rudolf Hoss, and the cyanide from the Zyklon B then got them all within 20 minutes.
From memory that was the early gas chambers which they have partially rebuilt and there are the hatches in the roof.
The later bigger ones at Birkenau had flase showers installed to fool the people that they were been disinfected but you are right, they still dropped the tablets in from the roof even with them.
http://www.deathcamps.org/gas_chambers/gas_chambers_auschwitz.html