So today I decided to chop off the last two inches of my Rubi Rails where they keep hitting my rear tire. To my suprise when I popped off the end cap, mud comes oozing out. I ended up with about a third a bucket of mud once I removed the rails and drained them out. Not sure how the mud accumulates in there so well but it really does!!!

I'd recommend popping off both end caps now and then and flushing out the rock rail tube with a hose.

 

Good info. Will have to check that out