I've got the new sending unit and fuel pump ready to go in my 1997 K1500 suburban. While taking it apart I had to scrape off the sealant. What type of sealant goes back on?

 

There isn't any sealant that I've seen... I'm guessing you had to scrape off the gasket that was under the three-pronged lock-ring that was on top of the tank? In that case, the "sealant" is actually a rubber gasket, and getting the lock-ring and the gasket back into place is a royal pain in the butt. Check RockAuto.com for good prices on the lock ring and gasket -- in my experience, you end up replacing the ring too; it's only a few dollars more.