garbage, rubbish, shaking, danger
圾 centers on waste and instability: garbage and rubbish are discarded, unwanted material, while shaking and danger suggest something unsteady or precarious. The meanings do not share one clear center; the character seems to cover both refuse and a sense of perilous movement.
圾 combines 土 (earth) with 及, which may contribute sound. The exact historical development is uncertain, and the connection between the components and the meanings 'garbage' and 'danger' is not clearly established.
Picture earth (土) piled up with something reaching it (及): a heap of garbage shaking dangerously, ready to collapse.
For ギュウ, imagine a pile of garbage that, when it shakes, makes a low 'gyuuu' groaning sound: gyuu -> ギュウ, like the earth itself is groaning under the rubbish.