Garage toilet drain

[steevyn]

I am adding a small utility room to my new detached garage that will contain a toilet and sink. The concrete has not been poured yet, so I am able to lay the drains before. The 4" PVC septic main is about 30 feet away downhill, and I have already dug that trench. I cut and glued the pieces for inside the garage, and then realized maybe I shouldn't have used 3". I've read some sites that say 3" only on upper floors, and some that say its fine anywhere. So that is my question, should I trash what I've done and start new with 4", OR could I used the 3" under he toilet, then convert it to 4" to run out to the main, OR am I ok to stick with the original plan and use 3" all the way. The toilet and sink are side by side in the corner closest to the septic, so they go immediately out under the wall. Also, what is the best method to connect to the septic main (rubber T, or pvc T w/ rubber coupler), and it's not meeting at an exact T or Y in the right direction, so I need to turn the drain slightly at the end, how should I do that?
Thanks!
Steve

[hj]

3" all the way is the normal installation. You make the connection using the proper fittings, do not "cock" the joints. Even more important is how you installed the pipe in the garage. That is where you can make mistakes, not in the pipe to the tank.

[steevyn]

I think I'm ok inside the garage. The toilet drain goes through the floor into a 90`, then straight to the septic, a nice straight shot other than its not hitting the main line how I had hoped. The sink goes into a 90` under the floor then into a Y behind the toilet. I'm putting a studor redi-vent in between the two. I've ran that past a plumber who said that all looked good. Everything appears to have a nice slope as well, but i will confirm that before backfilling.
Thanks!
Steve

[prashster]

Can u post a diag of the layout? I'm concerned about the vent for the sink.

I infer that you have the studor vent coming off the sink drain AFTER it goes into the ground. If you have a sink trap, you've then created an S trap. If yr sink drain is below the floor, then the drop is too long.

[steevyn]

Here is an actual picture I modified, this was before I leveled it up so it's very rough. I know its not pretty, but keep in mind it's just a utility room in a garage and I'm no pro. I wanted everything to be inside the room to prevent freezing within the walls (it will be framed and insulated when done). I will be using a 24X24 stand up laundry sink, so all the drainage will be hidden under it.




Here is where the lines meet in the yard, I would love any suggestions on the best way to put those together as well since it comes together at a bad angle!

[prashster]

Is that vent close enough to the toilet?

Sweep the connection to the main line as wide as poss.