Sucks to be you.Its metal.
I have had to do this on two different NX in the past.Both sat for over 5years so rust in the tand,the fuel pumps and sender units were caked up and clogged.
Heres what I did...and what you need
-Igo get some long thick rubber gloves like dishwashing ones that go up to your elbows,or be prepared to get a shitload of cuts on your hands and arms....with gas burning them!! I wish I did this.
-Jack up the front of the car or do this on a hill so the fuel is toward the rear of the car
-Use a sipohon or pump(cheap at harbor freight) to get out as much gas as possible.
-remove the whole pump and sender assembly completely so thew tank is empty.
-I used an old credit card for a scraper,and another plastic scraper I had to scrape all the rust off the tank walls,and bottom.Actually a little fuel helps loosen this syuff and eventually you will have handfulls of crap to scoop out.
-Little by little keep cleaning,and use a small shopvac(I have a 1x1)to suck out the rest.
-Put in a new fuel pump,and sender(used is ok) and throw out the crusty/rustsy stuff or you are asking for trouble.
-Reassemble the tank.
-Pull fuel line off at the filter or fuel rail and pump a couple gallons of fresh gas through the lines.I actually had to get injectors,too,they were clogged.
-You probably will need to clean the tank at least one more time after driving some miles.After the new gas swishes around,it will loosen more sediment and start to pile up by the sock again....ask me how I know this...LOL.
Heres a couple pics.have fun,but be thorough with your cleaning or you will regret it.