Why are your tortoise's feces white and runny?

This could be a sign of infection in your tortoise, or a symptom of internal cancer (depending upon your tortoise's age and health status). Regardless of the cause, loose faeces are not healthy and can result in your tortoise becoming dehydrated, which can be fatal if severe or prolonged enough. You may want to consult your veterinarian about treatment options for your tortoise as well.