Hand wash using warm soapy water to thoroughly clean your snackbox/lunchbox . Remove the silicone seal and wash it separately to ensure no nasties get left behind. Use a cleaning brush set to get into any small crevasses. Do not use abrasive cleaning agents or scourers as they may cause damage to your snackbox/lunchbox.
Alternatively, you can place the snackbox in the dishwasher (top rack only).
Allow to air dry completely before re-assembling.