How often do you clean it out?
I think, on average, I only remember to do it about once a year. My washing has not been coming out very clean lately so I grovelled about on hands and knees (ouch!) mopping up the spillage with an old towel and found:
Assorted screws
Various washers, plastic and rubber
Bits of gravel
Dog hairs
And at least three shredded cable ties.
I gave DH a ticking off about not emptying his pockets whereupon he picked up the washers, screws etc., rinsed them off in the tea strainer and put them back in his pocket. 
I'm mystified as to how it all got in there in the first place because I always check his pockets! 