when the water pressure isn't enough to get the gunk, i go to the craft store and pick up a packet of the thick pipe cleaners. they make some that are the perfect width for aqua clear tubes, and they bend easily enough to make it through. works great, and i can get a packet of about 5 of them for $1 US which lasts me forever as i just clean off the one i've used and use it until it starts to get a little scraggly looking. cheap and easy solution