It's the Baja Designs 1.5 gallon (about 6.5 ltr) tank that is made to fit the earlier model KTM EXC's.
I can't link the thread I did about the install of the tank but I can give it a bump if need more info.
Some men like the fish'n,
Some men like the foul'n,
Some men like to hear........
to hear the cannonball a roar'n!