I just had this issue recently. In the poseidon user guide (in your help: directory probably), called poseidon.guide, under the heading class drivers/printer.class it states:
In turboprint just enter usbparallel.device as the parallel.device to use and select the correct printer driver for it. That's it.
Weell.... for me I had to remove my printer driver, install it again, set port to device (turboprefs>Printer tab) and enter usbparallel.devie as the device (unit 0). The unit number is generated by trident - if you open trident anad look at the log it will tell you which unit number your printer is mounted at.
If you have a printer driver for your printer using vanilla printer.device you could also try changing the settings in prefs:printers to use usbparallel.device - it may work, it may not.
btw - usbparallel.device is generated runtime by trident, it does not need to be 'found' or installed in your devs drawer.
