What might cause a basin to gurgle at the end of draining?

A basin gurgling at the end of draining is often indicative of inadequate venting in the plumbing system. Proper venting allows air to enter the plumbing system, which is essential for maintaining balanced pressure. When a basin drains, water creates a vacuum that can cause a gurgling sound if the vents are blocked or insufficient. This blockage prevents air from entering freely, resulting in negative pressure that forces water to create turbulent flows, leading to the characteristic gurgling noise.

Other factors, such as improperly supported pipes, might affect overall plumbing performance, but they are less likely to specifically cause the gurgling effect during draining. An undersized drain pipe could lead to slow drainage or backups, but it does not directly contribute to the gurgling sound. Similarly, improper drain slope can lead to drainage issues but would generally not result in the vacuums created by inadequate venting. Therefore, inadequate venting is the primary cause of the gurgle sound during drainage.