Hello, I am installing a first floor bathroom and I need some help with connecting to the main drain. I am on a concrete slab and I already dug out the concrete and dirt. The opening is 2 feet wide by 6 feet long. The existing sewer line is 4 inch cast iron and it is 14 inches below the floor. The sewer line runs through the long end of my trench, that is, if you are looking down at the floor, you would see the exposed 6 feet of horizontal run sewer line heading to the street. The toilet will be a 12 inch rough in. The opening on the bottom of the toilet is 14 inches directly over and dead center of the underneath sewer pipe. Given that my trench is 2 by 6, what kind of run and fittings should I use to make the connection for the toilet and sink? Also where should the placement of vents go? This bathroom is on a sun porch with 9 foot high ceilings, so I have ample room to tie the vents together and run it out the roof. It would be easier than trying to tie into the main stack that goes out the second floor roof. Last item, I would like to have the toilet closer to the street than the sink. Not sure if that matters, but someone also mentioned something about a backflow preventer as well? I would appreciate any and all answers from anyone who is familiar with doing this type of work. Hopefully I described everything well enough. Sorry to not have pictures but any help is appreciated. Thanks.