Set the PaperBin Property of the Printer Object to an AcPrintPaperBin constant, preferably its value.
I would also suggest to keep your printer names and the associated PaperBin in a table. When needed, DLookup the PrinterName at the PrintersTable and get the AcPrintPaperBin constant.
Just remember to set the default printer and default PaperBin for the user running the script, back.