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
Salomon Speed 500ml Softflask Blue | Trekkinn
Salomon STD 28 500ml Softflask Blue | Trekkinn
How to clean water bottles, flasks and bladders | Salomon How to - YouTube
Budget vs Mid-Range vs Leader: Soft Flasks – All The Running Kit Reviews
How to Clean a Soft Flask - Home Explained
How To Clean Water Bottles, Flasks, and Hydration Bladders - We Are Explorers
HOW TO CLEAN WATER BOTTLES, FLASKS AND BLADDERS – Salomon Sports