It is almost certain that TG at DPS will refuse or be unable to check you in the following day for SQ flights ex. BKK. Bags might get checked through but you will be asked to collect your SQ BP's at BKK. Whether SQ will collect the 700 Bath dept. tax depends on whether it has already been collected when the ticket was issued - as suggested above - or if the SQ landside check-in staff doesn't notice that dep. tax has not been collected and fails to request payment from you. Anyway, have 700 B ready to pay for the dep. tax if you go landside on this itinerary.