I did this a few years ago: transited SIN on SQ with 4 months validity on Aussie passport on my way to Europe. Singapore consulate in Sydney confirmed no problem if just transiting SIN and SQ were able to check me in at SYD but emphasized that I would have to stay airside in SIN. It was a bit scary (I was on phone to consulate while in the taxi to the airport) but all okay in the end.