anyone involved in 3D printing ?? is a gas tank possible ?
If you are thinking thermoplastic FDM 3d printing like reprap/makerbot, then no, it's not going to work.
There are several issues. FDM printers usually have small volume, measured in a couple inches. The printing process is very slow, so even if you found a printer that can make something this big, it would take days if not weeks to print. Plastic is deposited in layers and it's pretty hard to get perfect fusion between the layers. I've printed toys for my kids and they usually don't even hold bath water. The materials used soften and melt at very low temperatures, for example PLA is printed at 180C, and can get soft just sitting out in the sun on a nice summer day. I don't know how the plastic would hold up against fuel, for example ABS melts in acetone.
Thermoplastic 3d printers are useful for making prototypes, but I would not make any functional part for a motorcycle where lives depend on it.
As others have mentioned there are different processes like laser sintering where they melt small metal particles together. It's also pretty slow and would cost more than outfitting a shop with all the tools necessary to make an aluminum tank.