On that visit to Auschwitz you mentioned he stood there with Hoess and determined that the North West corner of Birkenau was the most suitable place for the extermination apparatus.
That was a claim made by Hoess in his pre-trial statement "The Final Solution of the Jewish Problem at KL Auschwitz", dated November 1946.
However, serious historians have long recognised that Hoess's claims are untrustworthy, since they are irreconcilable with what we know about the development of homicidal gassing at Auschwitz.
In the above claim, Hoess states that after he received an order from Himmler in the summer of 1941 to establish an extermination centre for Jews at Auschwitz (which is known to be false), Eichmann came to Auschwitz, and together they identified two peasant houses as the places for the installation of gas-chambers.
In other words, the selection of the two houses (later Bunkers I and II) is supposed to have occurred BEFORE a gas was selected, BEFORE the experiements with Zyklon-B had taken place, BEFORE the conversion of Crematorium I in the Auschwitz main camp into a gas chamber, and even BEFORE the construction of Birkenau had started.
We know from other evidence the sequence of events leading to the establishment of homidical gassing at Auschwitz. First the camp staff carried out experiments in a building-cellar in Auschwitz main camp, using Zyklon-B to kill Soviet POWs. Then Crematorium I was converted to a gas-chamber, for killing Soviet POWs. Then a peasant house in the village of Brzezinka was converted to a gas-chamber; the exact date date is unknown, but it had occurred by May 1942. Finally, a second peasant house was converted to a gas-chamber.
The question is, if the two peasant houses had been selected as killing centres BEFORE all the above events took place, why were the experiments carried out in Auschwitz main camp and not in the two houses? Why was Crematorium I then concerted to a gas-chamber, rather than installing the gas-chambers directly in the two houses, which according to Hoess had already been selected for that purpose several months before?
The answer is that Hoess's claim is totally bogus. He was trying to divert responsibility for homicidal gassing from himself (and his organisation the WVHA) by loading it onto Eichmann (and the RSHA).