Abstract: A telescoping, U-shaped straight through, primary flow invert form may be lenghtened or shortened to meet the diameter of the cylindrical manhole and is mounted at opposite ends to the aligned main flow inlet and outlet pipes of the manhole. Longitudinally projecting bottom and opposed side invert tabs located at the ends of the straight through invert form contact the insides of the inlet and outlet pipes, respectively, to center the form. Slide guides, each carrying a retainer tab, adjust the retaining tabs longitudinally to position them within respective pipes at respective ends of the form for preventing lifting of the invert form during concrete pouring within the manhole. An angularly adjustable, intersecting side flow invert form projects from another pipe opening to the manhole at some angle to the straight through form and includes interlocking, axially slidable, opposed section halves.