My upcoming travel will consist of 2 separate r/t tickets with 2 carriers. On the last day of travel, there'll be flights involving both carriers in and out of BKK: GF into BKK, connecting to SQ out of BKK. If I explain this to SQ, will it waive my 700-baht BKK departure tax? (And if so, I won't be able to book online, as the departure tax would be automatically added to the fare.)