Too Much Coffee

I did my (bi-)weekly backflush yesterday. I always soak my PF together with the filter baskets in 1 liter of Urnex solution. After the usual scrubbing I tried to think of a way to clean the spout of the PF. I ended up using cotton buds (these things you use to clean your ears, although on the box it says 'do not use inside ear'!). The amount of black sticky oil deposits that was hidden there, you could not imagine! So I subjected the PF to a closer inspection and I noticed that although the spout openings are round, the inside of the PF is actually a rectangular box (if you know what I mean). So in the corners behind the spout openings a lot of dirt and deposits build up.

Although I tried to clean it for 30 minutes with cotton buds, I could not completely clean it. Any suggestions are welcome! Perhaps boiling the PF in hot water?

No wonder that you need to 'season' the PF after a backflush; so much detergent must be stuck there as well.

Try ovenspray. The stuff removes everything.
A very small and longitudinal brush (like a bottle-brush) from a shop for laboratory articles, as used for cleaning tubes etc helps also. MTBers for example use these kind for cleaning the tubes of their waterpacks (camelbak, Platypus, Source)