Stop Sewage Overflow Act This bill extends through FY2030 and revises a grant program that addresses stormwater and sewer overflows into rivers or other water bodies. Under the existing program, the Environmental Protection Agency awards grants to states, which in turn provide subgrants for projects that address the infrastructure needs for municipal combined sewer overflows, sanitary sewer overflows, and stormwater management. The bill reduces the share of the cost of grant projects that financially distressed communities must pay, increases the minimum allocation for green infrastructure and other environmentally innovative activities, and prioritizes grant assistance for municipalities with high levels of sewage in rivers, lakes, and bays.