Originally Posted by estnet

I don't know about UA but Thai does not allow passengers connecting from SQ to do this. They require that you go through immigration in Bangkok even if going on to an international ap in Thailand. You then have to go over to the domestic terminal to board!

If UA is the same 2 tips - if the bus connecting the 2 terminals is stuck in traffic jams (as it was on my recent trip) and took forever you can walk btwn the terminal INSIDE - go the level 2 (btwn arrivals and departures) - there is a covered indoor walk way. In any case you CAN check your bag through - but it may arrive in the "international" section at your final destination. Just walk over and pick it up.