Homebrewer here. We deal with plastic hoses all the time
- To get rid of mold, soak in hot water and fragrance-free Oxyclean. If that doesn't do it, use a brush or a piece of string with a paper towel on the end. This may not be super-helpful advice as you may not want to buy OxyClean just for this purpose.
- Avoid mold by always drying your hoses! Spin them like helicopter blades to get rid of excess moisture then hang down to dry so that both ends are hanging down
- Do not blow into your hoses, that introduces moisture and bacteria
- Avoid putting anything with sugar in your bladders
-