Plastic reservoir with a cap behind rear shock (2001 Fazer 600)

[vladman]

Hi, I was poking around the bike and for the first time (in 6-7 years ownership) noticed this!  :rolleyes

I have no idea what it's for.  It's NOT the rear brake fluid reservoir (I know where that is).  Can anyone advise on what it is?  I can't see the level in it (it's got the usual max and low markers), it's quite dirty, but I think it's low, or even empty.  Wouldn't be surprised, as I've had the bike for a long time, and never even knew this thing was there!

I can post a pic if my description is not clear.

Thanks!