One of the first things that happens when a home is being built, is the basement bathroom plumbing is installed. This is done as soon as the footings and foundation are poured and the forms are stripped off.

Sometimes the gravel will be laid before the plumbing and then the plumber has to dig a trench in the gravel so the pipes will be at the same level, and even with, the top of the gravel.

Having just finished our home I learned this fact right up front. The hole is dug, the footings and foundations are poured, and then the plumber comes and puts in the plumbing pipes.

The plumbing lines have to be sloping gradually downward, so that gravity will help the flow of water and sewage as it flows towards the final destination, the city sewer line or your septic tank.

With the use of flexible plumbing pipe, many of the abrupt right angles can be avoided, which might cause a buildup and eventually a clog in the line. For basement plumbing pipes that are underground and under cement, usually cast iron or plastic pipes are used.

The plumber will only take the sewer line out 18 inches or so beyond the footings of your home, where your excavator will need to connect and lay the remainder of the sewer line, which connects to the septic or city lines.

Every sewer line has to have exhaust lines which also helps the flow as gravity pulls the sewage gradually to the point of destination.

Once basement bathroom plumbing lines have been installed, then the cement flatwork can be poured. If mistakes are made, then plumbers often have to jackhammer up the cement and make changes, but it's obviously easier to do it right the first time.

People who own their own homes and then want to put in a basement bathroom have other options of pumping the sewage and waters up to the exit line, or cutting into the existing line if it is below the cement floor.