The blue liquid in the Porta Potties is not really a disinfectant so it doesn't get rid of the germs in the Porta Potty.
But instead the blue liquid that is put in Porta Potties is put there to make the Porta Potty smell fresh and clean for up to seven days, and hide the contents of the tank.
It just helps the Porta Potty smell fresh and clean before they empty it because without the use of the blue liquid those Porta Potties would stink so bad that no one would want to use them.
So that's all that blue liquid is. It's simply put there in the Porta Potty tank for freshness and smell and to hide the sewage in the tanks because without the blue liquid the porta potties would not be desirable to use.