Which structure within the pelvis is responsible for storing waste until elimination?

The rectum is the structure within the pelvis that is specifically responsible for storing waste until elimination. It is the final section of the large intestine and serves as a temporary storage site for feces. As the digestive process concludes, waste material is pushed into the rectum, where it can be held until the appropriate time for defecation.

In contrast, the urinary bladder primarily stores urine before it is excreted from the body, which involves different waste products than those stored in the rectum. The urethra is the conduit through which urine or, in males, seminal fluid is expelled from the body, but it does not store waste. The ovaries, involved in the reproductive system, do not play a role in waste storage; instead, they produce eggs and hormones. Thus, the rectum is the correct answer because of its specific function in the waste elimination process.