Here is a quote from a private letter of 21 June 1942 from Walter Foehl, deputy head of the Department of Population Management and Welfare of the General-Gouvernement, to his "SS comrades" in Berlin.
Every day we have trains coming in with more than 1,000 Jews a time from all over Europe. The medics patch them up, and we either house them here temporarily or mostly ship them on into the Ukrainian marshes, in the general direction of the Arctic Ocean, where - assuming they survive (which the Jews from the Kurfuerstendamm or Vienna or Bratislava certainly won't!) - they are all being collected together to await the end of the war, though not without having built a few autobahns in the meantime. (But we're not supposed to talk about that!)
The letter is in the Federal Archive/BDC, personal file of Walter Foehl, and is quoted on page 135 of the book "Architects of Annihilation", by the German leftist historian Goetz Aly.