The two similes "loose drains clack-clacking like castanets" and "all the alarms...crying their needs to the night like babies waawaaing" create vivid imagery that emphasizes the noisy, chaotic atmosphere of the scene.
The first simile compares the sound of loose drains to the clacking of castanets, which are percussion instruments typically used in Spanish flamenco music. The comparison creates an image of a constant, rhythmic sound, as if the drains are providing a musical accompaniment to the scene. The effect of this simile is to emphasize the cacophonous nature of the environment, and to create a sense of disarray and disorder.
The second simile compares the sound of alarms to the crying of babies, with the repetition of the word "waawaaing" adding to the effect. The comparison creates an image of the alarms as being helpless, vulnerable, and in need of attention, much like a crying baby. This simile emphasizes the urgency and intensity of the situation, as well as the emotional impact of the alarms on those who hear them. Overall, both similes contribute to the sense of chaos and confusion in the scene, while also creating powerful and memorable images in the reader's mind.