Replacing cast iron pipe and adding new toilet

Question

I'm planning to add new toilet/shower/sink downstairs. I have one existing on the 2nd floor and right under I'd like to add the new one.

The new one is on the concrete slab, so no basement underneath which makes the work more difficult.

The iron cast pipe goes along the wall and I'm planning to cut it and replace it with PVC all the way up to the existing toilet, plus I will add the new toilet to it.

My question is, since the second toilet is going to be on the concrete slab, is this going to work if it's on the same level as the connection will be? Or does the connection needs to be below the toilet drain. If so, how much below it needs to be so the flushing and draining works properly. Thanks

Do I really have to do the 2nd option and cut out the concrete or 1st option would be ok if I use saniflo, pump. Do I still need to tilt the drain down from sink and shower if the pump used?

Answer 1

The first option is if you have absolutely no choice. It could possibly have continuous issues, and you might eventually have to do choice #2.

You need at least a 1/4" decline per linear foot. For long runs I like to add an inch if I can. So for a 20 foot run I would put it 6 inches under from shower trap. Note that you probably need to do no digging for your sink. Pipes can probably line in the walls fine.

For the shower you need to break up concrete - about 1-1.5' wide and dig down to lay pipe. Fill area with gravel and concrete over it again. This is not a seriously hard job. A jackhammer makes it maybe a couple hours and can be done with a sledge hammer. Probably the hardest part is throwing away the concrete. With the slope for your shower your toilet should be fine joining the main stack probably right above the shower.

Also note that I don't see any venting in your picture.

Note: I am not anti-saniflo pump. I have had to use them 2-3 times over the past 20 years. I didn't feel good either time and I seriously doubt the original pump is working in those locations. For this instance it would take more time to hook up the pumps to both the shower and the toilet, cost a lot of money, and have serious long-term money/time spent in making sure these systems were working. I would be done breaking up the concrete and laying line (and maybe concreting over) before you got done reading the saniflo manual. It is just the "easy" way out of your situation and is actually MUCH harder. If it were just a toilet I would still say no way but I might be more on the fence, the shower makes breaking up concrete a no brainer. I am just offering the best way to do this at the lowest cost and work. If saniflo is preferred please note that it isn't the easiest way and will cost more money and time. (please read customer reviews - they are all over the place)