Which of the following are common signs of a clogged drain system?

Gurgling sounds and foul odors are indeed common signs of a clogged drain system. When there is a blockage in the plumbing, air and water cannot flow freely, often creating a gurgling noise as the build-up causes air to be trapped. This noise can become particularly noticeable when water drains from sinks, showers, or toilets. Foul odors emanate from stagnant water and decaying material in the pipes, which can result from organic waste that has collected in the drainage system. Both of these signs indicate that the drainage system is not functioning properly, and prompt attention is needed to prevent further issues.

In contrast, options referring to bright lights, clean drains, fast flow, or the absence of sounds or drainage issues do not signify problems commonly associated with clogs. Clean drains and fast flow indicate that there are no clogs present, while no sounds and no drainage issues suggest that everything is functioning optimally.