Timely thread; I have a similar question.
Flying HAN-SIN on SQ in September. Arriving ~17:30 and departing the following morning ~06:00 on UA, SIN-HKG-ORD-IAD. HAN-SIN flight is on a separate ticket from my UA itinerary.
Will SQ be able to check my luggage all the way back to IAD at HAN? Can I stay airside at SIN overnight?