Urinal deodorizer blocks are small disinfectant blocks or tablets that are added to urinals. As these products originally contained para-dichlorobenzene (pDCB), they may also be called para blocks. Besides disinfecting, the purpose of these materials is to deodorize restroom urinals. They are placed above the urinal drain, often in the confines of a small plastic device called a urinal screen that prevents loss down the drain when they dissolve down to a small size.