It's important to clean your baby's bottles as soon as you can. The longer the leftovers sit, the harder it will be to clean in the long run. You also want to make sure to clean the bottles instead of just rinsing them out thoroughly. Invest in a quality bottle brush to ensure you get into all of those crevices.  In addition, if you know if you won't be able to clean your bottles right away, keep them in the fridge until it's cleaning time. This will slow down any bacteria's growth inside the bottle and make it easier to clean once you are ready.  Finally, if you don't see a difference in the cleanliness of your bottles, it might be time to switch to glass bottles. They are much easier to clean than silicone and plastic bottles, and you'll probably be more satisfied with how clean they look. Just be careful if your little one tries to handle the glass bottles.