Always ask for a transfer/fare receipt, even if you are not going to transfer. Transfer/fare receipts are valid for 90 minutes.
sfmuni.com has a text description of the 23-line
23: Riders east of Third
Trips cross 3rd Street at Palou in the Eastbound direction, then turn around at Griffith St. and terminate at Palou and 3rd Street.
Buses and F-line: Always ask for a transfer, even if you are not going to transfer to another line.
