‘scooby Snacks’ Coming From Hose?

My buddies setup seems to have a bunch of small chunks coming out of the hose under med/hard draws. We washed out the hoses, stem, bowl, vase, and valves the night before and allowed everything to dry prior to use.

Any ideas on what causes this? Unfortunately I don't know the brand of hookah or anything, nor if the hoses are washable. While we are on the subject, what is the difference between a washable and unwashable hose? He seems to think they are all washable, regardless and I don't know what to think. I guess you can run water through and let any hose dry right? But is there more to it?