I feel silly for only just realising, but the whole cap from the Salomon soft flasks comes apart allowing you to give them a good clean : r/ultrarunning
Drink Tube Cap - 42mm | HydraPak
Gregory DryLock Magnetic Bite Valve | REI Co-op
Nathan ExoDraw 2.0 18oz Insulated Water Bottle - Men
Bite Valve Sheath 2-Pack | HydraPak
Salomon Soft Reservoir 1.5L - Hillmalaya
The 5 Best Running Hydration Packs | Tested by GearLab