TX Gobbler

Hello all! New to the board, and I need some help! I just bought the recoil reducer for the Nova pump. This may be stupid of me, but where does the chunk of black rubber tubing go? Is that something that I need to cut to fit to size and put in with the mercury cylinder? If so, does it go in before or after the cylinder? I feel really stupid having to ask this, but I cannot find any installation instructions. I cannot find my gun manual. Thank you for your help in advance. I appreciate you.