I am adding a new bathroom in the basement. Is there a special order that toilet, lav. And shower should follow left to right 1 2 3, the left being the last fixture to the street ? What are the proper sizes I should be using to tie into 4" main with these 3 units? Can I tie and vent shower to lav, and all to toilet? 3 into 1, or should I tie into the main with 3 separate Y's ? Looking through the clean out, the main appears to be about 18 inches from top of concrete. Toilet, lav. and shower would be 3-5 ft. from main. How fast should all this fall to the main? I am sorry with all the questions,this is all very confusing.
Thank you... Rick

if I'm going to design it, I would be using a 4" main all the wall to the water closet in a wye pattern where the end must be a floor clean out wyed to a 4"x2" for venting. before it goes to the water closet il install a 4" x 3" Y-branch and connect a 3" x 2" Y-branch each for lavatory and shower. The end of this branch would be a vent branch, where it is connected to pipe up from the lavatory and shower vent. Don't forget a floor drain near the water closet and importantly the p-traps. There would be no particular order as you have said, it is the convenience of design that governs, the pipings will just find its way, as efficient as possible(there are many ways to kill a cat). A 1% to 2% would be best for your slope. I'm a designer and not consider myself an expert. I cannot advice you man, some experts here are angry if somebody advices anybody else besides them. I hope you understand. I'm only telling what I would do, if I'm in your shoes. (in case they will read this).have a nice day. Happy renovating.

" I'm a designer and not consider myself an expert. I cannot advice you man, some experts here are angry if somebody advices anybody else besides them."

No Nick! Some experts around here get angry if they have to step in and keep correcting the bad advice that you post. So far I've had to correct you three or four times. And if you get pissy with me one more time you're out of here. As you say you're not a plumber and youi've proved that point to my satifaction with some of the advice that you've posted. If anyone doubts me just go back and read some of Nicks advice. Ya did pretty good here Nick, a little wordy but all in all pretty good. Much better then your other posts.

Rick, Let me show you a typical basement bathroom group rough in. This configuation only uses one vent for the entire group.
4" from the toilet to the main. The lavatory to connect to the toilet drain line with 2" and vent to the roof or revent back in the attic to a existing roof vent. The tub/shower to connect to the lavatory drain line with 2" and be wet vented by it as will the toilet. Make your slope 1/4" of fall to each foot of drain line. Be advised to always check local codes before changing or remodeling your drainage system. If you need more details click on back. Good luck, and Nick , I'll tell you this one more time. It can cost the askers big bucks if they follow bad advice on the technical pages such as, plumbing, AC, electrical, etc. I'm not out to bust yo chops. I'm trying to protect the askers. You start giving better advice and I'll get off yo back. Be aware that I'm not the only one that's looking at your posts. I'm just the most vocal. Cheers and get away from that keyboard and out in the fresh air. Tom