Small vertical drop in the middle of a horizontal branch

[Tony1997]

Hello-
Thank you in advance for this awesome forum and all the help and knowledge that goes around.
I'm trying to run a 3" toilet drain horizontally between the joists for about 2 feet until it passes over a perpendicular (to joists/drain) wall at which point it needs to drop below the joists and take a 90 degree turn and go for about 4 feet toward the main stack (main is inside the same wall that the pipe passes over) and then turn another 90 (or maybe 45) toward the wall where it connects to the main stack via a 90 vertical elbow. to my understanding it needs to be vented before any vertical drop even a 6" drop, correct?
My questions:
- is it ok to drop a horizontal branch for let's say 6 inches at once mid way?
- is it ok to have two horizontal 90deg turns few feet apart like I described above (they'll be long sweep 90s or double 45s)?
-should I use long sweep(or 2 x 45s) fittings for where it drops under the joists? I might be able to use a 90 or even 45 turned half way to go under the joist and pick it up with another 45 for the rest of the horizontal run.

Your opinion would be greatly appreciated.

 

[wwhitney]

Hello-
to my understanding it needs to be vented before any vertical drop even a 6" drop, correct?

Not for a WC, as it has an integral trap that is meant to siphon and is refilled by the tank. Yes for any other trap; to avoid siphoning, the vent must be connected before the trap arm falls more than one pipe diameter.

The UPC does require venting the WC fixture drain within 6', measured from the closet flange along the pipe run.

Your questions:

1) Sure, as long as you comply with the above venting requirements.
2) I don't think your description has two elbows in a row, both of which are horizontal to horizontal transitions?
3) For horizontal to horizontal, or for vertical to horizontal, you need a LT90 (or two 45s). For horizontal to vertical, you can use a regular quarter bend.

If I understand your narrative correctly, to minimize bends you could use:

Closet flange - V(ertical) pipe - closet bend - H pipe (between joists) - 45 to start falling (rather than quarter bend) - maybe short pipe, maybe a street connection - LT 90 - H pipe (parallel to wall) - LT 90 with outlet at a 45 degree angle to the wall - 45 or wye to connect to stack.

Or if you need to keep the pipe tight to the joists at the stack connection, you could do LT 90 with outlet horizontal - quarter bend or san-tee to connect to stack.

If it's OK to be below the joists before crossing the wall, you could just put the closet bend outlet below the wall top plates and skip the vertical jog after the wall.

And as mentioned previously, somewhere in the first six feet of pipe you need your vent connection.

Cheers, Wayne

 

[Sponsor]

 

[Tony1997]

Thanks a lot Wane. You quickly answered all my questions. And you are right, the elbows I mentioned were at the drop site so they aren't horizontal to horizontal. I will have it vented within the 6' required length. Thanks again for your speedy response.
Cheers.