I am trying to be helpful by editing the question into the format that seems to have the most success at getting answers.

I saw a few problems with the original.

The biggest is that it wasn't clear. It is good to have one clear claim that you are skeptical about. It wasn't clear which of the following statements you were doubting:

* Washing hands prevents disease.
* Washing hands prevents disease from faecal transfer.
* Washing hands prevents you from getting a disease from others.
* Washing hands prevents you from getting a disease from yourself.

or perhaps something else.

The reason I think this is important in this question is because:

1) I strongly suspect washing your hands isn't merely about washing off whatever got onto your hands during your bathroom trip, but also whatever got on your hands since the last time you visited the bathroom.

2) There are plenty of studies, going back to Ignaz Semmelweis in 1847, showing hand-washing has practical results, but there may not be many studies showing how to use the bathroom without handwashing.