Hi:
I own a XT660Z since last saturday, it is time to start mods
Snorkel Out.
A visit to the local plumbing store ended with a rubber than fits either a WC

or a XT660Z filter cap.
Placed on the filter cap.
And installed on the bike.
I will remove the cover in a few days in order to check that it works as expected, but it looks GREAT!!!.
Excuse my English, I'm spanish.
have fun,
j.