Should I be worried about a longitudinal crack in our cast iron sewer line?

A crack in cast iron combined with a belly is a double whammy that usally means the whole line is compromised. Cast iron rots from the inside out, so if you are seeing a visible crack on the exterior, the bottom of that pipe is likely paper-thin or allready gone. It is not just a leak risk; it is a structural failure. Once the pipe loses its integrity, it can collapse under the weight of the soil, especally under a heavy structure like a patio.

The belly is actually the bigger headache here when it comes to repair options. While **CIPP lining** or pipe bursting can often save you from tearing up that patio, those methods generally cannot fix a low spot. If you line a pipe that has a belly, you just end up with a lined pipe that still collects standing water and solids, leading to constant backups. To fix a belly properly, you usually have to dig it up to regrade the soil and reset the pitch.

Since the line is under a covered patio, you definatly want the plumber to see if they can access the line from both ends to attempt a trenchless repair, but be prepared for them to tell you that at least the section with the belly needs a spot repair involving a jackhammer. If the crack is near the foundation, they might have to dig inside the house or right at the footer, wich adds a massive amount to the labor costs.

Whatever you do, do not let the sellers fix it themselves. They will hire the lowest bidder who will slap a temporary patch on it just to get through closing. Get a firm quote from your own plumber for a full replacement, and make sure it includes the cost of restoring the patio if they have to cut into it. Ask for a closing credit or a price reduction instead of a repair. A failing main sewer line is a massive leverage point because most lenders will have a hard time with a house that has a compromised waste system.

I had no idea you couldn't just line over a belly. If the heavy concrete patio is what caused the pipe to sag in the first place, won't a brand new pipe just do the same thing eventually? Also, if the plumber is allready there with a camera, can they check the pipes inside the house too? I'm worried that if the main line is rotting, the stuff under the bathrooms might be in the same shape. This is way more stressful than the paint colors we were originally worried about!

If that patio is structural or has heavy piers, you might want to ask your plumber about tunneling. Instead of cutting through your nice concrete, a crew can dig a horizontal shaft under the slab to replace the bad section and fix the grade. It’s more labor-intensive but saves you from having to match old concrete or ruin the patio's look. Also, make sure the camera tech checks for channel rot along the bottom. If the bottom of the pipe is gone, pipe bursting can sometimes fail becuase the new pipe won't follow a straight path. It's a mess, but better to find out now before the toilets start backing up.