Installing drain and running water lines under concrete

Hello all, any advice is greatly appreciated!
I am in the process of adding an in-law suite in my basement. Adding a small kitchenette. I've trenched through the slab to the bathroom to connect the new kitchen sink to the existing drain line from the shower. 2 Part question below:

1. I think I am going to replace the three way sanitary T in the picture with a 4 way T to accommodate the new pipe from the kitchen sink. The pipe leading down into the existing T is from the bathroom sink, and pipe coming from the right of the picture is from the shower drain. These pipes are cast iron and I will be splicing in a PVC connector. Is replacing this 3-way connector with a 4-way connector the best way to add this new kitchen sink drain line to the existing drain? Is there an "easy way" to cut cast iron pipes? I was planning on using a reciprocating saw. Please let me know if I am missing something or setting myself up for failure.

2. Second part of the question...The two vertical copper lines behind the drain pipes are the hot and cold water lines for the bathroom sink. I was planning on tapping into these and running PEX tubing to the kitchen sink location. Multiple questions here...Can I use PEX tubing in the dirt under gravel and concrete? What kind of connector should I use where I splice into the hot and cold lines (considering this connection will be eventually covered in dirt and concrete as well)? Should I run the PEX tubing in some sort of rigid conduit to keep it from collapsing?

Thanks for the help. Please feel free to poke holes in my plan and offer any suggestions. Obviously I am not a plumber, just a homeowner with a DIY background.

thats not a tee, its a combo. if you replace a combo with a double combo. you need to see if the combo you are replacing is DEAD level.

because, if one side of the double combo is raised, the other side is backfalling. so to answer your question,,not a good idea.

remove old combo,,replace it with new, add a wye and a 45 for new drain..buckle them in with cast iron x plastic mission bands

use pvc


do not splice into the water line under the floor, loop the pex up into a wall, tie in above ground

no joints under concrete

Frodo nailed it using a wye with a 45. The existing combo servicing the bathroom sink should not be touched. That is an old technology using lead and yokum joints. Breaking the seal and causing a leak will create a nightmare for you to fix (you may have to yank out everything and reinstalling all new piping). To the left of that combo I see cleanout. That may be your best bet to make the tie-in somehow. As for using a reciprocating saw to cut cast iron I'm not sure it will cut it but you could try. A chain cutter is usually what I used to cut cast iron pipe. Good luck and keep us posted on the progress.

I just thought of something. The cleanout is probably connected to another combo. See if you can remove the cleanout and use a sanitary tee to sit on top of the combo below. From there you can run your kitchen sewer line into the sanitary tee. Note that for waste line purposes a sanitary tee can be used upright (it cannot be laying down like a combo).

Thanks for all the advice!

One follow up question in regards to tying into the existing hot and cold water lines. These lines run through about 6" of concrete underneath the wall that they run up into. So if I were to tie into them within the wall I'm not sure how I would be able to run the lines back down through the wall and into the trench without tearing apart the wall and demoing the concrete underneath it. Is soldering in a copper tee into these lines in the dirt under the concrete not a viable way?

solidering under ground is against the UPC code..you can SILVER SOLIDER but not soft solider

drill a 1'' hole, thru the wood and the concrete with a roto-hammer drill. you can rent one for a day...25 bucks

or, bring it up outside the wall..

the reason no joints....foundations move, they are like a living thing,,,they contract and relax

if your copper is soft solidered the stress will pull it apart sooner or latter.

silfloss 15% will not pull apart.

BUT>>>SILFLOSS is a whole nether game...pipe must be CLEAN and you heat it till REDHOT

Ok so I did as Frodo suggested as far as the drain lines go but when I tested it it leaks from where the rubber couplings meet the cast iron. I used an angle grinder to clean up the cast iron pipes as much as possible but they are still kinda rough around the outside. Is there a better way to clean up these pipes to get a good seal with the rubber coupling?

Also, I did what you said and ended up running the PEX up the wall and will make my connections to the hot and cold water lines within the wall.

vgaler said:

Ok so I did as Frodo suggested as far as the drain lines go but when I tested it it leaks from where the rubber couplings meet the cast iron. I used an angle grinder to clean up the cast iron pipes as much as possible but they are still kinda rough around the outside. Is there a better way to clean up these pipes to get a good seal with the rubber coupling?

Also, I did what you said and ended up running the PEX up the wall and will make my connections to the hot and cold water lines within the wall.

Click to expand...

this will seal it, its a cast iron band sealant. good stuff!!

Thanks Frodo! I apply it to where the rubber meets the cast iron right? Should I apply any glue to where the rubber connects to the PVC?

should not need anything on the pvc..but you can put some of that on their also

that stuff is like liquid tar...buy some rubber gloves and a 1'' paint brush

throw away after use...if you get it on you. diesel wash's it off


welder used to jump my butt for sticking my hands in the fuel tank on the welding machine

Someone suggested getting a carbide grinding disk and trying to clean up the cast iron some more. Think this is worth a shot or will the Black Swan take care of all that?

cut the cast with the grinder,,,clean it with a wire brush,,,or rag

slap sum blk swan on it, call it a day