The pollen-stained tube is pretty hard to clean - tried all types of cleaners before giving up and just making a new tube:


Old tube was held to entrance reducer-block with a few screws:


Here's a view of the entrance with the reducer slide in it: it gets screwed with this side out into the window block with the holes lined up (the window block is essentially a block of wood filling the bottom of the window with a hole drilled into it). It was getting a bit of mildew, even though it doesn't really get exposed to the exterior, so I melted and rubbed some beeswax into it: