What you need to consider is that the fuel tank is full of crud. Did you
run it near empty recently? If so,I bet you usually keep it more than a
quarter full. When a crudded up tank is run very low(less than a gallon)
the crud gets concentrated and  more can get into the filter. When using a
fuller tank, the crud gets spread out and less dirt gets a chance to go
into the little hole at the bottom.The crud can float around for
years,doing no harm, if you keep the tank full.

 I once found about a cup or two of rust flakes in my tank.Big thick
flakes. I had just changed the filter only 20 miles earlier.This was my
parts van that got a weekly run around the neighoborhood.Of course the
filter could not be the problem.Wrong!! The filter was filled up to the
top with flakes.The pump howeled. this tank was usually kept almost
empty.Dont know how the flakes got there.