You need to be in your dashboard - find the promotions manager on the left. Inside the promotions manager it gives the option for the port sales - the price is $10.00 for a week/until sold now.
I've sold a few partial ports on there - be prepared for a lot of low offers. Your best bet is to price it at your lowest possible price and if anyone gets close to take it.
If you don't mind selling over a few weeks time - start by offering a 20% off promotion for a day, then up to 25% off, then 30% off, 35%, 40%, etc. This is the best way to maximize what you get back.