I am in the process of laying out a rough plumbing diagram for a small accessory building.

I have attached a drawing of my proposed design. The structure will be a on a concrete slab.

Plumbing will be for a small bathroom (WC, Shower, and Sink) and a utility sink outside the bathroom on the same wall. There will be one "wet wall" framed with 2x 6 lumber.

My questions:

Is it OK to vent the Shower using the sink standpipe/vent? These fixtures are less than 5 feet from each other.

I am planning for one cleanout outside the structure between the slab and the connection to the septic line. Is this the only cleanout I need? The length of the drain pipe is less than 35 feet.

Is is OK to connect the WC flange and vent stack directly across from one another (ie using a cross tee) or do these need to be offset from one another (either upstream or downstream?

Picture below. Any comments are appreciated. Thanks

Hi CMMC... Start out with a full size cleanout to grade either outside of house (within 18" or so of foundation) OR if your local code allows put the main cleanout just inside bathroom...not attractive but they have cleanout covers that look nice when tiled up to...depends on your area and how deep pipe is outside....Point is you MUST have a main cleanout first before any other work can be added. The full size cleanout must be in direct line with the main run of the main drain line..cannot be on the run of the wye fitting.

OK...all connections underground must be made via wye fittings only...there are exceptions...but not for you here..ok?

All vent fittings must roll above the centerline of the wasteline to be considered a valid vent connection.

OK...here is what I would do...I would run the main run as you have pictured...I would install a 3" wye so that the branch of the wye picks up the toilet... between this 3" branch and the toilet elbow I would install a 3x2 wye fitting (rolled above center line as mentioned for vents) and then pick up the left sink with that toilet vent (called a wet vent)...must remain 2" as you have drawn all the way to the 3" vent stack.

Now, out of the run of that 3" wye (the wye with branch to toilet) I would reduce to 2" pipe and run the vent up 2" to right sink and then pick up the shower drain exactly as you have drawn (vent must connect within 5 feet of shower drain p-trap... if not will need to pipe it within 5 feet and run back to the sink abit less direct... ). Again, remember to roll that wye above centerline as well.

When you penetrate the floor with any vent add a full size dandy cleanout (called a test tee) should you need to rod/snake a drain later... they come in handy sometimes... just something I started doing... especially on tub vents... here, I install a dandy cleanout above flood level of tub and then if tub clogs I just pull out plug and send snake down without having to drain/clear tub... BUT I DIGRESS!! ;)

Anyway... you are looking pretty good. If you want to redraw and submit I will be glad to get back to you. Hey, if this helped please RATE the answer by clicking on button below! Thank you. Hope I was clear.

MassPlumber2008 - Greetings and thanks for the review. I will redraw and repost later this evening.

However, just to make sure I understand your comments :

You are suggesting that the drain pipe (starting to the right of the WC WYE connection) be reduced from 3 to 2 inch. This 2 inch pipe would then connect into the sink to the right of the WC and also the Shower.

Also, what about the WC 3 Inch vent? I understand about the WC Wye with the elbow extending to the WC bend. Where would the 3 Inch vent be positioned off the drainline for the WC. (ie upstream, downstream or directly opposite of the EC Wye).

Thanks for your help - I will rate and repost shortly.







Hi CMMC...Start out with a full size cleanout to grade either outside of house (within 18" or so of foundation) OR if your local code allows put the main cleanout just inside bathroom...not attractive but they have cleanout covers that look nice when tiled up to...depends on your area and how deep pipe is outside....Point is you MUST have a main cleanout first before any other work can be added. The full size cleanout must be in direct line with the main run of the main drain line..cannot be on the run of the wye fitting.

OK...all connections underground must be made via wye fittings only...there are exceptions...but not for you here..ok?

All vent fittings must roll above the centerline of the wasteline to be considered a valid vent connection.

OK...here is what I would do...I would run the main run as you have pictured...I would install a 3" wye so that the branch of the wye picks up the toilet...between this 3" branch and the toilet elbow I would install a 3x2 wye fitting (rolled above center line as mentioned for vents) and then pick up the left sink with that toilet vent (called a wet vent)...must remain 2" as you have drawn all the way to the 3" vent stack.

Now, out of the run of that 3" wye (the wye with branch to toilet) I would reduce to 2" pipe and run the vent up 2" to right sink and then pick up the shower drain exactly as you have drawn (vent must connect within 5 feet of shower drain p-trap...if not will need to pipe it within 5 feet and run back to the sink abit less direct...). Again, remember to roll that wye above centerline as well.

When you penetrate the floor with any vent add a full size dandy cleanout (called a test tee) should you need to rod/snake a drain later...they come in handy sometimes.....just something I started doing...especially on tub vents....here, I install a dandy cleanout above flood level of tub and then if tub clogs I just pull out plug and send snake down without having to drain/clear tub....BUT I DIGRESS!!! ;)

Anyway...you are looking pretty good. If you want to redraw and submit I will be glad to get back to you. Hey, if this helped please RATE the answer by clicking on button below!! Thank you. Hope I was clear.

OK... you understood drain going to shower... BUT

You do not need a three inch vent off the toilet.. only a two inch vent... AND THAT PICKS UP THE SINK ON LEFT as a wet vent. Go back and reread how I said to pick up toilet... after the branch of the 3" wye for toilet you install a 2" vent between wye and toilet elbow.. again that picks up sink on left as a wet vent... do not need 3" vent...UNLESS YOU DO NOT HAVE A 3 inch vent through the roof already...but I am sure you do...so will only need a 2" vent and then connect all vents together and run up 2" and connect to vent upstairs... get it..?

I assumed three inch was present... if not there.. do not pipe it in!! Get back

MassPlumber2008 -

Thanks for the reply (you are a patient individual) -

I should have clarified in my previous post. No plumbing exists today. This is a layout for a standalone farm structure. The positive it that I can lay it out however it would be easiest and the least complicated. The negative is that it will go in/under a yet to be poured slab, so I want to make sure I get it right.

I have attached a revised drawing.

If you look at the revised drawing, (Starting from left to right). I have 5 green rectangles that would represent WYE connectors coming off the main drain pipe.

I believe I understand your comments. The one outstanding question I have regards the WYE Connector being positioned between the WC WYE connector and the WC Flange. (I did not draw this one, but I understand it to replace the WC vent WYE)

I understand you to say that I would not need rectangle number one (left to right). I could vent the left sink using the WC vent. This would eliminate the left most dashed vent line - correct?

Where I am struggling is - If I put a WYE connector off toilet elbow, wouldn't I then have to cross back over the 3 inch Drain Pipe to tie it into the sink vent? Or are you saying that the sink does not need a vent pipe (ie no pipe would be extended above the height of the sink. I would cap the left most sink PVC at the top of the stub out).

To further convince you that I am thick - why does they recommended WYE connector for the toilet wet vent come off the WC elbow? Why wouldn't it come off the main waste pipe in between the WC and left most sink.

Thanks again - I REALLY appreciate it.



OK...you understood drain going to shower...BUT

You do not need a three inch vent off the toilet..only a two inch vent...AND THAT PICKS UP THE SINK ON LEFT as a wet vent. Go back and reread how I said to pick up toilet...after the branch of the 3" wye for toilet you install a 2" vent between wye and toilet elbow..again that picks up sink on left as a wet vent...do not need 3" vent...UNLESS YOU DO NOT HAVE A 3 inch vent through the roof already...but I am sure you do...so will only need a 2" vent and then connect all vents together and run up 2" and connect to vent upstairs...get it...??

I assumed three inch was present...if not there..do not pipe it in!!! Get back

Yes! God bless you... correct!! You do not need rectangle #1.

OK... further, and you are following me just right here... the 2" vent for the toilet needs to run back to the sink on left and come up through the concrete...you do have to cross 3" but that is the way it goes!!

You asked why.. Because if you run the left sink inline you will effectively cut out the wet vent from toilet when the shower drains... think about that... by running two inch vent to pick up sink at the branch of the toilet, shower waste can run by without disturbing the toilet vent... that make sense?

Let me know if not clear, but you seem to be following just fine... ;)

GOT IT! Thank you very much for your help - I rated your answer. I also appreciate it very much. Cheers.





Yes!! God bless you...correct!!! You do not need rectangle #1.

OK...further, and you are following me just right here...the 2" vent for the toilet needs to run back to the sink on left and come up through the concrete...you do have to cross 3" but that is the way it goes!!!

You asked why...? Because if you run the left sink inline you will effectively cut out the wet vent from toilet when the shower drains...think about that...by running two inch vent to pick up sink at the branch of the toilet, shower waste can run by without disturbing the toilet vent...that make sense??

Let me know if not clear, but you seem to be following just fine...;)

Applauding!! Good luck!