That is a Hayes tank, among my favorites and certainly worth using. The internal clunk line will almost certainly be the original black Neoprene gasoline or glow fuel line. There is no reason to change it unless it is visually damaged.

The procedure for removing the tanks hard plastic plug is very quick and simple. Remove the fuel line from the black plastic nipple and use a pair of slip joint pliers and grasp the black plastic plug (not the nipple itself) with the pliers held inline with the nipple. using a gentle rocking motion you can pull the plug out with the pickup line and clunk still attached will follow the plug out.

To reinsert the clunk, line and 0 ring hard black plastic plug. Insert the clunk assembly and plug up to the 0 ring. Use a socket wrench that will slip over the nipple and up to the plug. Now you can use a small mallet to tap the plug assembly back in without damaging the nipple.

Unlike most other tanks you can remove and reinsert the plug assembly an indefinite number of times with no leakage. I have many Hayes tanks in service and have never needed to replace the 0 ring.

John