This is what I've been doing: open report in designer, go to File-Print, go to 'Preferences' and set the duplexing for my default printer driver ("print on both sides") which is a totally different printer than both printers that the users are printing to. Then I choose "Printer Environment" to check it and then edit 'expr' for only duplex=2, and empty 'tag' and 'tag1'.

I tried following your instructions, I go to preferences of my default printer and duplex is already set(it's always has been duplex), then I take a look at the Printer Environment and it's unchecked already.