Thread: mudguard fell off

Hi,
Yesterday avo when I got to work I found that they had closed off the grass/dirt section of the parking area because of the rain.After figuring out where I was going to park,I managed to pull my right side mudflap completely off . I DO have big mudflaps...
Thats not a problem fixing /putting them back on.But when I looked underneath this morning I found that I had taken this cylindrical bit off one of the hoses.Its seems to recide next to the filler pipe.Is it the breather pipe?
What is it and whats it for? (sort of smelt like diesel,but wasnt strong diesel smell).
Beast drove home last night no worries.

Thanks

cheers