Transgenders and Public Bathrooms: Where Should They Go?

Performing the bodily function of relieving oneself is generally considered a private matter. In the case of a multi-use facility, males prefer to be with males and females prefer to be with females. But in the case of the transgender, which sex do you came? Your birth sex or your adopted sex? And should it matter when you enter a public bathroom? What should be the rule whe it comes to transgender individuals and the use of public toilets? Should companies and schools be required to install a unisex toilet? Or would that get too costly