Hans-Ulrich Obrist has organised exhibitions in his kitchen, in a library, in hotels, and on board an aeroplane. This series of projects on the periphery of the exhibition circuit has now been consummated in the toilet. His exhibition in the Museum der Stadtenwässerung (Drainage Museum), a barracks on the outskirts of Zürich full of lavatory bowls, toilet brushes and sewerage maps, completes this cycle of shows designed to parallel the alimentary process, which began in Obrist's little St Gallen kitchen in 1991.

On that occasion Christian Boltanski, Frédéric Bruly Bouabré, Hans-Peter Feldmann, Paul-Armand Gette, C.O. Paeffgen, Roman Signer, Richard Wentworth and Peter Fischli/David Weiss produced metaphors for the intake of food. Now various artists including Gilbert and George, Hans Haacke, Ilya Kabakov, Nancy Spero, Allan Kaprow, Mike Kelley, Maria Eichhorn, John Miller, Fabrice Hybert, Otto Mühl and Gerhard Richter have dedicated themselves to all things involving defecation. Their artistic irrigation neatly parallels the processes at work in the nearby sewage plant. Dominique Laporte may well have noted that since the 16th century, civilisation's imposition of ever stricter taboos on waste products has led to a sublimation of shit, but he didn't know that water could be purified of leftover food, cigarette butts, nappies and condoms and pumped back into the mains supply.

The artists in 'Cloaca Maxima' do, on the other hand, know that what comes out at the rear goes back in at the front. In art at least, we have proof that the public has a private origin. Obrist suggests that art 'opens up possibilities of oscillation from the public to the private, and frees excrement of its negative connotations'. This is impressively illustrated in Ilya Kabakov's reconstruction of a Russian communal lavatory. From behind the shit-smeared toilet door comes the sound of melancholy singing. Unlike his documenta installation The Toilet (1992), this work isn't a blanket denunciation of the Soviet state as a whole, but positions the toilet as a refuge from daily socialist life.

Compared with Kabakov's poetic work, Boltanski and Fischli/Weiss made the art equivalent of a solid bit of plumbing. Boltanski glued swimming objects into the toilet bowl, and Fischli/Weiss installed a rather joyless television film set down the tube. Stephen Pippin placed a bug in the museum toilet, and the gurgling of the toilet-flush surged from the loudspeaker by the entrance like a force of nature. It wasn't exactly the reserved English way, but it was funny. At the other extreme were Andreas Slominski's disturbing bananas, injected with the artist's urine.

Gilbert and George paraphrased the digestion process with an imaginatively assembled menu. Gette, Richter, Kelley and Miller produced photographs on the subject; Carsten Höller hung a washing line on the adjoining garage, draping white skirts diagonally into the room; and Peter Fend hoisted his version of the Swiss national flag at the entrance of the grounds.

Can 'Cloaca Maxima' be seen as an eco-exhibition, a collection of recyclable Anal Art? Obrist combined the artistic works with displays and posters from the museum's collection, freeing the art from the dead end of autonomy and placing it in its sociocultural context. Lavatory bowls from the baroque to the present day and monstrous wastepipes created a scatological cabinet of curiosities. Outside the museum, guided tours led through the sewage-works to the stench of the underworld. Here too are plenty of curiosities: the tomato pips that have spilled out of the filtered slurry, for example, were already sprouting into new plants.

An exhibition about shit wouldn't be complete without its own digestion problems. Otto Mühl, the Viennese artist who was sentenced to seven years imprisonment for child molestation after a kind of show trial, was invited to participate in 'Cloaca Maxima' out of a misguided sense of solidarity. His installation of a so-called 'scatological altar', relegating Duchamp's and Manzoni's artistic achievements to the dungheap of art history, was unadulterated shit.