Keef, the blue tank is also an Acerbis, 25 liters for the later RD02s. But some idiots tried to paint it, I found 2 layers of blue and if those tank don't want something, it's being painted. I tried to remove the paint, but couldn't do it. Also, the tank gassed out so much you got nauseous sitting on the bike.
So, sadly, I had to look for an alternative. Bigger tanks for the Domi are awefully hard to come by. So I just fabricated new mounts for my old tank.
Re:K&N; like Thor said, it's cheaper in the long run. Also, I wanted to uncork that poor thumper so I did the whole deal (and removed the secondary air system). I didn't ride her before all the mods, so I don't know the difference. But she does feel very crispy now.