NIDAQMX Python - Setting an output to High Impedance (High-Z) on USB-6001

I have a USB-6001 and need to toggle an output between '0' and 'High-Z' and have tried the following methods with no success:

1. Using an analog output
   1. ao_output_impedance=1.0e9. I get error message that this option is not available on my device
   2. ao_voltage_current_limit=0.0. I get error message that this is also not supported.
      
   3. So how can I turn off an analog channel?
2. Using a digital output
   1. First I do 

       chan_fast_en_l= task_do.do_channels.add_do_chan("Dev1/port0/line0",line_grouping=LineGrouping.CHAN_FOR_ALL_LINES)
       task_do.write(True,auto_start=True); 

   2. chan_fast_en_l.do_tristate

      This has no effect and also gives no errors. The documentation says I must 'commit' this change, but I don't know what a 'commit' is and failed several attempts like "task.action.commit=0".

   3. chan_fast_en_l.do_output_drive_type=DigitalDriveType.OPEN_COLLECTOR;

      I get no errors but the pin continues to output 3.3V
   4. Is there a write keyword like TRUE, FALSE, HIGH-Z?

I'd really appreciate some assistance! If you could help for digital and analog, with some sample code, then that would really help me and others I'm sure.