Urinal deodorizer block

As these products originally contained para-dichlorobenzene (pDCB) they may also be called para blocks.

[clarification needed] Para-dichlorobenzene- and naphthalene-based blocks do not readily dissolve in water/urine, but easily sublime into the air, creating a sickly-sweet odor that has anti-microbial effects.

[2] Many urinal blocks are now para-dichlorobenzene and naphthalene free; these water-soluble alternative blocks are made from a mixture of fragrances and surfactants (normally quaternary ammonium compounds),[1] which offer some active cleaning and antibacterial efficacy.

Some recent formulations also include bacterial spores which, coupled with the surfactant cleaning power, can more completely get rid of odors and blockages caused by the buildup of solids in the traps and pipes.

Some manufacturers claim that these "biological blocks" can enable completely no-flush waterless urinals to be fitted.

A pink deodorizer block + urinal screen in a urinal at Georgia Southern University
A Johnson Suisse waterless urinal with a block placed above the drain at City University of Hong Kong
Para block