The answer to 'why is my sewer line low water pressure' is that there could be a blockage or obstruction in the sewer line. This can cause a restriction in the flow of water, leading to low pressure. Some common causes include tree roots, debris buildup, or a broken pipe.
Symptoms of a sewer line blockage may include slow draining sinks or tubs, gurgling sounds from plumbing fixtures, or sewage backing up into the home. If the issue is localized to one fixture, the blockage is likely in the drain line for that fixture. But if the low pressure is throughout the home, the problem is likely in the main sewer line.