HuskeeCups need to be cared for differently than ceramics or glass as they are a much softer material. Please follow the below advice to ensure you have longer-lasting cups.
The most hygienic way to clean HuskeeCups is to put them through a dishwasher. This ensures they are washed at a minimum temperature and duration to correctly sanitise. Just make sure there aren't any sharp objects loosely packed with HuskeeCups, as under the water pressure they are likely to bounce around and damage them.
If you do not have a dishwasher you can manually sanitise by following advice from the Australian Food Standards here.
A damp microfibre cloth (or similar soft cloth) with a small amount of detergent can be used to help remove stubborn marks.
A toothbrush is useful for cleaning around the lid.
For stains or odours, soak in a tub of hot water with 1 tsp of espresso machine cleaner per cup, for 8 hours/overnight.
DO NOT use abrasive cleaners such as a scourer as this will permanently damage your cups.