New Basement Rough-in

Well, I had a new house built last year with the intention of finishing the basement this year. The basement is rough plumbed but the wife wants to have 2 bathrooms instead of one and a mini-kitchen including a sink and possibly a dishwasher. I've finished a couple other basements but this will be the first one that I have to move/add significant waste plumbing. Can I start with a few questions? I'm attaching a picture to hopefully make this a little easier..
1. Is there an easy way to figure out which way the pipes run under the concrete? There is a stack toward the upper left of this picture so I figure the main goes that way.
2. The existing vent goes from the floor 2" and then transitions to 1 1/2" PVC about half way up toward the ceiling. At the ceiling it goes to the left in the picture about half way. To me it looks like I can rough in the sink on the right to the vent, T off of the vent to the floor for the kitchen sink (bringing the waste to the main), install another T where it comes out of the ceiling and extend it to the other bathroom sink on the left (bring the waste to the main). Does this sound reasonable? Will I need to put in more vents for the tub and toilets or should that do it?
3. I'll need to break up the concrete to move the toilet and tub rough in anyway for the bathroom on the right. I wasn't planning anything interesting here. Just taking a look and moving them with 45 deg elbows if possible making sure the trap at the tub is still above the main. Any suggestions on an easy way to plumb the tub and toilet on the left? I'm assuming that I can bring the toilet directly into the main and the tub to the run that I'm making for the toilet.
Any help would be appreciated...
Rick

The first thing you are going to have to do is get someone in with a line locator to find out where your main drain is. Then the rest of the questions will be more easily answered.

My guess is that the main runs from the far upper left hand corner of the drawing (about 14' off of the drawing) toward the existing toilet rough in. They are building a house similar to mine so I will check it out if I can. Any suggestions on the venting of the other items?
Thanks,
Rick

I was thinking something like this....

Comments? Help??

piping

Your drawing is good as a concept, but the way you actually install the pipes, since there is more to it than what your drawings show, will determine whether it is proper or not. You could not install the piping exactly as you show it.

I'd appreciate any comments or suggestions that you would have.... I've never done any substantial waste plumbing. The location of the main is pretty close according to looking at another house like mine.

Questions:
How do I determine if the vents are adequate?
Do you always put the vent downstream of the other items coming into the main?
Which fittings do I use?
Thanks,
Rick

Can someone explain what is "flat venting"?
Thanks,
Rick

Oh...I looked up flat venting. There is no intention to flat vent. Here is a schematic where I tried to do it 3D. There still is the problem with not enough vent size... Comments?

pipes

Neither tub or toilet is vented according to your drawing.

Is that because the vent is not close enough? Please explain.
Thanks,
Rick

the vents should be before the discharge..for instance on the tub. You have a 2" trap arm of "x" feet developed length. You need the vent on that trap arm within 5' maximum of the trap (or 8' depending on your code ) and at least 2 times the pipe diameter away from the trap minimum (4"). Also on your drawing those 3" san tee's...assuming that's your main, those are illegal. The have to be combo Y 1/8 bend fittings or similar.

To answer your next question (cuz im a mind reader) anything below the flood rim of a fixture has to be a waste fitting, anything above can be a vent fitting.

and..lol

are those two 2 inch vents at the top tying together and being reduced to 1 1/2? If anything where 2 vents of the same size meet the pipe should be increased.

the double san tee by the kitchen and lav there, would be illegal here again check your code. You may have to use a double fixture fitting.

vents

At the very least they should be connected to the tub drain lines so the water flowing from the toilet would not create a suction and pull the water from the traps.

Thanks hj. I'll do that. Since I'm not going to have enough vent size for everything down there, can I run a vent off one of the main stacks over to there? What fittings do I use?
Rick

I took a look at the stack. I have a 3" stack not far from the second bathroom area. Can I use it to vent the second bath? It already has a 1/2 bath from the first floor and a full bath from the second floor on it.

I also have one more option if I absolutely need more vent size. I had the builder run a 4" piece of PVC from the basement to the attic for later wiring if I needed it. I could use all or part of it for a vent all the way to the attic but the path would be torturous since it's on the other side of the basement. It would have to jog up and down across the basement ceiling. Comments?