| SEPTICTANK | Underground chamber in which sewage is decomposed by anaerobic bacteria (6,4) |
| SEPTIC | --- tank, container for sewage to be decomposed by anaerobic bacteria (6) |
| SEPTICTANKS | Containers where sewage is disintegrated by bacteria (6,5) |
| SPECTRUM | Word for the band of colours into which a beam of white light is decomposed, as seen in a rainbow; hence any array, range or scale (8) |
| SILO | An underground chamber in which a guided missile is kept ready for firing (4) |
| CESSPIT | Hole in the ground into which sewage flows (7) |
| GOUGHSCAVE | A 377ft deep underground chamber in Cheddar Gorge (6,4) |
| CLOSTRIDIA | Anaerobic bacteria that cause botulism and tetanus |
| BIODEGRADE | To be decomposed by living organisms |
| SILOS | Underground chambers in which missiles are kept ready for firing (5) |
| METHANE | This gas, which has the chemical formula CH4, is often produced in wetlands when anaerobic bacteria decompose vegetable matter. |
| BIODEGRADABLE | Describing an object that can be decomposed by living organisms, thereby avoiding pollution (13) |
| STRONGROOM | Specially-designed chamber in which valuables are locked for safety (10) |
| LACTICACID | Substance produced by the anaerobic fermentation of carbohydrates (6,4) |
| SALMONELLA | Anaerobic bacterium |
| WINECELLAR | Lower chamber in building new, I recall (4,6) |
| BROOMSTICK | Means to get to Hogwarts chambers in two seconds (10) |
| CAMERAOBSCURA | A darkened chamber in which images of outside objects are projected onto a flat surface by a convex lens in an aperture |
| CAISSON | What is a watertight chamber in which underwater construction work can be carried out? (7) |
| CYLINDER | Tubular chamber in which a piston works in an engine (8) |
