Is it normal for a plumber to add a $1,300 change order for a slope issue?

Texas code generaly focuses on the minimum fall—typically 1/8 to 1/4 inch per foot—to ensure solids don't settle, but there isn't a strict universal maximum slope for a short horizontal-to-vertical transition in a residential line. The concern about 'too much fall' ussually refers to the velocity of the water potentially outrunning the solids, though in practice, a steep drop into a main line rarely causes an actual blockage. If this is an existing configuration they are just tying back into, many municipal inspectors in North Texas will grandfather it in since the footprint of the repair is limited to the broken fitting. You shoud ask the foreman to cite the specific section of the local plumbing code they are worried about. If they can't point to a number, they might be over-engineering the fix or trying to recoup the $1,200 discount you negotiated on the front end. It is true that a camera inspection doesn't always reveal the exact vertical pitch of a pipe buried in clay; you don't get a clear sense of depth or angle til the dirt is pulled away. However, $1,300 for a few more feet of tunneling is a steep jump when the crew and equipment are already under the slab. One way to handle this is to tell them to proceed with the wye replacement as originally quoted and schedule the **rough-in inspection**. If the city inspector flags the slope, then you have a documented reason for the change order and you pay the extra money. If the inspector passes it, you saved yourself thirteen hundred bucks. Most inspectors are reasonable about repairs to old cast iron or PVC under a slab becasue they know how invasive tunneling is.

Keep in mind that $4,800 for a turnkey tunnel and wye replacement is actualy a very low price for this region. Most reputable shops won't even crawl under a house for less than $6,000 because of the liability and physical labor involved. They might be looking for a way to make the job profitable now that they've seen the actual conditions, but you have every right to see a failed inspection tag before you start digging further into your backyard.

I went through this exact thing last summer. My guys tried to hit me with a $1,500 "grade correction" once they saw the clay. I told them to just fix what we agreed on and I'd deal with the inspector. Guess what? The inspector didn't even pull out a level for the pitch; he just wanted to see the new PVC and the hangers.

These guys usually bid low to get the job then "find" problems to make up the margin. If they're already under there, digging three more feet is maybe two hours of grunt work. Don't pay for "potential" problems until someone with a badge says it's wrong.

I’m a bit skeptical that they actually need more tunneling just to address the pitch. Have you ruled out using a 45 or a sweep at the joint to transition the elevation within the existing hole? It seems like a lot of extra digging for a problem that can usually be solved with a different combination of fittings. If they saw the line on camera, they had to have seen the depth change. I'd ask why a simple offset won't get them to the right angle before you let them keep digging out your foundation.

Update: I mentioned using a 45 sweep to transition the elevation, and they actually agreed it would work without more tunneling. That saved me the $1,300, so thanks for that tip! However, they're now claiming the existing cast iron is too thin to clamp onto properly. Does that sound like another upsell, or is old pipe really that brittle?