The sink and tub drains connect to the septic line.
Septic lines, or waste drainage lines, are an integral part of the home's plumbing system, which consists of water supply lines, ventilation pipes and drainpipes. Adding an upstairs bathroom usually increases the value and marketability of a house. Plumbing the septic line in a new bathroom is a matter of tying in to the main vent-and-soil stack, directly or indirectly. Consult your local building authority before starting to ensure that it's permissible for you to plumb the new bathroom.
Instructions
1. Plan the drainage configuration to accommodate all the bathroom fixtures in the simplest layout possible. The septic line is a 3-inch line that runs from the toilet to the main vent-and-soil stack, but the drain lines from the sink and the tub/shower should intersect the septic line. If possible, arrange all the fixtures along a common wall.
2. Set a 3-inch toilet flange in the floor where you want the commode. If the walls in the home consist of 2-by-6 lumber, you can install a 4-inch flange and run a 4-inch septic line. Most houses, however, have 2-by-4 wall framing, so a 3-inch flange and 3-inch lines are necessary.
3. Connect a 3-inch PVC elbow sweep to the toilet flange in the floor between the joists. This is a 90-degree elbow but it turns gently to reduce the risk of clogs. When you connect PVC fittings, use PVC cleaner and PVC glue in the fittings as directed by the manufacturer.
4. Measure from the elbow sweep to the stud wall and cut a 3-inch PVC pipe, with a pipe saw, to match. Install the pipe to the opening of the elbow sweep attached to the toilet flange and install another elbow sweep where the septic line turns to fall vertically between the wall studs.
5. Grade the septic line. This means the drainage line must slope downward at the rate of 1/4-inch per foot. If the toilet is 8 feet from the wall, it will drop 2 inches between the toilet flange and the elbow sweep in the wall. The weight of the pipe will usually pull the end down, but if it's too steep or too shallow a grade, secure it at the correct height with a metal strap, wrapped around the pipe and nailed to the wall studs.
6. Tie in the sink and tub/shower drainpipes. This depends upon the bathroom layout, but these 2-inch drainpipes must connect to the 3-inch line running from the toilet. Use 3-inch to 2-inch reducer sweep T-fittings to attach the smaller drains to the larger line. In some cases, the two smaller lines will connect before reaching the septic line, leaving only one pipe to connect to the 3-inch line.
7. Run a 3-inch PVC pipe vertically down between the wall studs and tie the 3-inch line into the main vent-and-soil stack, which is usually at least 4 inches in diameter. The vent-and-soil stack is the vertical pipe that attaches at the bottom to the horizontal sewer line and exits the roof at the top. Between those two points, all the septic lines and the vent lines will attach to the stack, with the vents attaching above the level of the septic connections.
Tags: septic line, elbow sweep, 3-inch line, toilet flange, vent-and-soil stack, main vent-and-soil, main vent-and-soil stack