I also have an old cast iron sewer line under concrete that I have been dealing with for 40 years – my thoughts & input for you:
-> I think you can successfully use it as-is. You have professional feedback that the pipe is intact, has no roots, and it is sloped acceptably. The scale is an unfortunate nuisance (my pipe looks like yours), but periodic maintenance has helped me avoid back-ups.
-> For maintenance, about 6 years ago I found some rather low-cost pressure washer accessories on Amazon that greatly help:
- 50-ft 3/8” hose, >3000psi.
- A nozzle with various orifices: one that sprays forward, and 4 that spray radially at 45 degrees backward, and spins the front of the nozzle. It pulls itself through such that you have to restrain it, and cleans very well!
- A lighted fiber-optic that I taped onto the hose. I have impressive video of the action!
- Long Gloves!
Caution – The pressure washer is for periodic maintenance - not for blockages. If you trap high-pressure water it is going to splash right back on you – trust my bad experience!
-> I also have low-flow toilets. As a precaution, I use multiple flushes when there is a big load.
-> If this is a main line, also consider that the kitchen waste can also greatly contribute to blockages. Oil and grease will ‘freeze’ on the cold cast iron. The build-up is impressive and hard to remove. I have learned to greatly limit food products going down the drain, and use cold water to rinse dishes off.
-> Your floor drain puts you in an unfortunate situation, but it gives you access to the sewer which is critically important! An idea to eliminate the back-up is to find a floor drain insert that has a built-in check-valve to keep sewer water and gases within the pipe.
Q: Do you even need a floor drain? If not, then you can simply cap it with an expandable insert that sits flush with the floor. These are available at Lowe’s / Home Depot for about $8, and you maintain easy access.
