There are two toilets at the ISS, both Russian-made — one in the US module and another one in the Russian one.
In addition, there are toilets in Soyuz ships docked at the station but they are used when the ship is in flight and only rarely when it is docked.
According to ISS commander Luca Parmitano, the toilet in the US section constantly signals that it is not working, while the one in the Russian module is filled to the maximum.
Later on, an engineer of Space Center Houston told ISS сommander Luca Parmitano that a toilet in the US module was operational again.