Yup! i also have the same problem though! But i have some solutions!

Glass bottles like this:

Firstly, the black/brownish stuff must be cleared, if not your hammy will drop fur!

2 Solutions :

1. Use a Q-tip/ Cotton Bud to clean out when you wash the bottles

2. Use a water guard: ( i use this, and so far its pretty good!)

Aristopet is pretty good too! It has vitamins which has helped countless of hairless hamsters, and a fab hutch cleaner for small pets!

Another brand which is cheap and good is ALEX! It has affordable ranges of awesome smelling mineral blocks and really quiet hamster running wheels too! Treats are always bought for my hammies too

To end of this post :

TADA!

My super cute darling says HI! <3