I clean out my lint filter after each load but then I too heard about vacuuming the part under the filter that opens into the dryer & the hose. We don't have a slim enough attachment for that so we called a company that only does that type of cleaning. After he cleaned it all out, right out to our outside exhaust ~ he had maybe a tiny fistfull of lint, maybe the size of an egg.

He did say "oh, you must clean out your filter often?" Yeah, after every load?! Doesn't everyone? So I'm thinking that maybe you have more of a chance of accumulating more lint if you don't clean your filter after each use?

I don't know but that cleaning that I had, was after 9 years of daily use at a minimum of 2 loads a day!
I did see this Christmas that they had those very slim vacuum attachments to clean out your dyer lint at Bed Bath & Beyond. They were also for sale at the Home & Garden Expo that came to Detroit too. (Along with the 'dryer balls' but that's another thread, right?

)
Oh...I do remember that the dryer cleaning man (I don't know what else to call him?) said that we had the good type of hose that was hooked up to the outside exhaust. We used to have the thin foil looking accordian type hooked from dryer to outside exhaust but we had it replaced with a different type ~ thicker & looks like metal ~ not sure exactly what it is though. He said those flimsy ones can catch on fire very quickly.