Ditto , I use the Por15 and I too have poured the excess back into the tin and it stay's fluid . Words Dave Smith, American Car Magazine, April 2016.... There's nothing you can do with the leftovers, you just have to wait for it to set then throw it away, which seems a shame. ? Obviously has money to throw away :-D I have had mine on the shelf for at least 6 months .
also in their FAQ'S Quote :
3. Pour in the entire can of POR15 Fuel Tank Sealer and “roll” the tank around so that the inside of the tank is completely coated. Then drain any excess for at least 30 minutes to ensure that the sealer has not “puddled” in the tank. After you’ve done this, pour the drained sealer back into the can, but Don’t Put The Lid Back On The Can Tightly Or It May Explode! ..really