The answer to 'why is my pipe overflowing' is that there is likely a blockage or clog in the pipe, causing water to back up and overflow. This can happen for several reasons, such as a buildup of debris, hair, or other materials in the pipe, or a more serious issue like a tree root intrusion or a collapsed section of the pipe.
Some common symptoms of an overflowing pipe include water pooling around the drain, a gurgling or bubbling sound, and a foul odor coming from the drain. If the overflow is in a sink or bathtub, you may also notice the water draining slowly or not at all.