We would be a bit surprised if any manufacturer of genuine composting toilets claimed they had never had flies in one of their toilets. There are a large number of dung fly species in the UK and due to their small size they can fairly easily find their way into a toilet vault. However, we are pleased to report that owners of our toilets very rarely report any problem with flies. It they do it is usually because the vault contents have become too wet. This might be due to inadequate maintenance for the level of use and can usually be resolved by a change in the management regime. Dung flies are not likely to act as disease vectors because they are not usually attracted to food.