Septic Tank Elimination: Does it make sense to install new toilet drain pipe?

[amateur plumber]

Thanks for the help.

The city just installed new sanitary sewers in my area. I am about to solicit a contractor to connect me to the stub. I have two drains to connect. 1) A 3" PVC line that drains the kitchen sink, and the washer in the basement as soon as I plumb a line to connect it to the PVC line. 2) a 4" cast iron (I think) line that drains my bathroom toilet, bathtub, and shower. The bathroom vanity drain disappears into the wall and I can't find where it drains.

My questions.

1) Am I correct that the drain is cast iron? (see photo)

2) Does the vanity drain into the cast iron pipe vent? That is the only structure that goes near the wall where the drain exits the cabinet.

3) Where will the PVC and the cast iron tee together to attach to the stub? Any recommendations?

4) Should I have a check-valve installed in the line to the sanitary sewer to prevent backflow? How long before such a valve fails?

5) The house was built in 1956, so I assume the cast iron drain is 55 years old. Should I consider replacing that line? I read that life span for cast iron is 60 - 100 years. The line was never heavily used (2 people) and has never had any problems.

Thanks for your help and corrections to my amateur terminology.

[cacher_chick]

If the city sewer can be connected out where the existing holding tank is, there is no reason to change anything in the house at all.

I would re-do it only if the new sewer were coming from a different direction, as eliminating unnecessary turns in the line is a good practice.

[amateur plumber]

The new city connection is far from the existing tank, so there will be a new line required. Question is should I replace everything back to the toilet drain connection.

[jimbo]

I see no indication you need to do any wholesale replacement of piping inside the house. I would listen to the recommendations of your plumber ( probably get more than 1 bid) as to the most expedient way to run the connection.
Most areas I have experienced, there is no need for a backwater valve. There are cases where it IS a good idea, and that often involves a case where street drains connect to the sewer, causing occasional overloads. Also depends on exactly where in the 'big picture' you are connected to the sewer. Contractor and city sewer department might have recommendations.

[Ramon Leigh]

I would question the need or wisdom of doing anything. I would never hook into city sewer that
will provide me with yet another monthly bill, unless the septic system is having problems that
require extensive work.

[amateur plumber]

Thanks for the replies. Next question is how should the contractor connect to the main drain once they have cut it. The first quote I got stated they would use a Fernco connector. Is that to code, and is that a good connection method?

[cwhyu2]

That is okay and as long it is done properly.It is code approved here for underground connections.