Can you catch flu from not washing your hands after going to the toilet?

In general, the answer is no.

The bacteria and viruses in the digestive tract and faeces will not give you the cold or flu.

However, if you are using a public toilet, someone with a cold or flu may have left viruses on door handles or other public surfaces and you could pick these up on your hands, transfer them to your nose and mouth and this may cause an infection in your upper respiratory system.