So what you’re saying is that your Bidon is not performing as well as it used to and should be replaced with a younger, fresher version?
^^deserves some recognition.
I have some bottles that are water only and others that are allowed filthy sports powder in them.
The strategy for me is to rinse them immediately (outdoor tap) when I get home, then scrub them with a bottle brush and got water ASAP, and then put them through the dishwasher. That just about does the trick, leave them too long (like a day) and it becomes a challenge to sort them.
Also don’t underestimate the value of a large opening bottle, not only for tipping powder scoops in but also for access, getting in there to clean with a brush after a ride.
All the above applies if I end up having to use a squash/juice mix instead of powder.