Busting Concrete and replacing Cast Iron

I had posted this over at John Bridge, but I thought I would post here since it involves plumbing, tiling will be later.

I finished busting up concrete ( remind me not to do that again! ). Actually it wasn't that bad once I got the hang of it. I rented a Hilti and it went pretty well.


It appears that there are many small pieces of 4" cast iron, and a 4" cast iron trap for the shower. The good news is that all of the sections appear to be connected with neoprene donuts

The first picture shows the toilet flange at the top and the shower drain ( a 4inch cast iron trap ). All of this will be getting replaced.

Now the questions:

1) I am planning on replacing everything that is exposed with PVC Should I replace the cast iron Y connection in picture 2 or leave that and replace from there.

2) Is the vent placement in this picture okay? it is after the toilet. It seems like I should have a vent connection before or right at the closet bend. The current configuration doesn't have a closet bend, the toilet pipe drops directly into the horizontal 4" pipe.

3) Do I just need to fill with gravel, compact and then cement, or will I need to drill the cement and use some sort of dowels to connect the new cement to the old.


I'm pretty sure of what to do, but always like a second opinion.

Thanks,
Ron

It wouldn't take too much to drill some holes and put in some rebar dowels to help keep the new patch from sinking or lifting in relation to the original.

pipe

The two questionable items are the toilet connecting to a tee on its back, (if that is actually the way it is done. The pictures are not too clear about that), and the 2" vent connecting to a sanitary tee on its side. You will probably have a very difficult time removing the pipes from the fittings.

T on it's back

Currently the toilet is connected with castiron using a 4" T in the main drain line. The toilet flushes directly down into this. Is this something that should not be done. I don't really want to change the main 4" pipe so that it is not a straight line.

-Ron