View Full Version : Single to Double vanity

05-27-2011, 04:51 AM
I have been reading the posts on this site for many years and have found the discussions not only educational but entertaining. I'm changing my single sink to a double sink vanity. I've done my research and Figure 3 is what I think I need to do for a properly draining, non-smelling bathroom based on a modified Terry Love design. This will all be buried in a non-load bearing wall of a 8 year old house. Have I used the right combination of ABS tee and wye fittings for the job?
At first I was going to use a double wye but I'm afraid of making a "S" trap situation. Secondly, I have no room for a cleanout in or under the vanity.

This illustration represents the current lavatory / vanity set up.
13106Figure 1 This is the current set-up as performed by a licensed plumber.
Figure 2
Is going to 1 1/2" pipe for the left tee going to create problems? 13107
Figure 3
I think that this is my best option. I think the 3" tee is going to drain better, help prevent clogs and be a better vent.

Providing that you find no faults and approve of my plan... I ask if the extra 3" drain run going to perform it's function better than going to 1 1/2" as in Figure 2 or will I just be throwing my money down the drain? What do you think?

Thank you and cheers.

05-27-2011, 05:01 AM
Picture # 2 looks just fine,no need for the extra 3 inch.

05-27-2011, 09:38 AM
Figure 2 is all you need, and even that is "overkill". If this is a bath on a slab floor, then the 3" should have a cleanout tee below the sink connections. A back to back fixture fitting, NOT a double Y NOR a sanitary cross, will accomplish the task without a lot of repiping.

05-27-2011, 10:11 AM
I vote for the double fixture fitting, 2" x 1.5" x 1.5" x 1.5"
Or figure 2 works too, but with more fittings.
Really the only reason for figure 2 would be if you only had a 1-1/2" pipe to start with. Since you have a 3" line, all of your possibilities are open to you.

05-27-2011, 01:38 PM
Here it would probably have to be 2 x 2 x 1 1/2 x 1 1/2 since it may also be the toilet's vent.

Good point. I wasn't thinking downstream about the possiblity of it being a toilet vent.

05-27-2011, 02:47 PM
Thank you for your help.

The double vanity that replaces the single vanity is a 350 pound beast. The master bathroom is on the second floor over a garage that has the spray foam insulation on the ceiling which not only provides a continuous vapour barrier, it also inhibits access to the pipes and drains. There's an 3" (at least) ABS vent sticking out of the roof immediately over the area in question and I ruled out the cleanout because there's no room for it...

Now, If I understand you correctly, you are saying that figures 2 & 3 will work, but it's over engineered for the task but I'm not sure what your suggestions mean.


Or are you suggesting that I can lose the vent as well?


Would the 3/4" rise over 3 feet potentially create an S Trap in either scenario?
Which one, if any, is correct?

Thank you, mfl

05-28-2011, 09:52 AM
Bump. Can anyone help me out?

Thank you

05-28-2011, 09:57 AM
Standard grade is 1/4" per foot.
As long as your trap arms are this long are shorter, you are fine.

1.5", 42" long trap arm
2.0", 60" long trap arm
3.0", 72" long trap arm

05-28-2011, 01:58 PM
Figure #6 is perfect, if you do not need the vent riser to be 2". And since it is a second floor you do not need a cleanout in the 3" riser.

05-30-2011, 05:20 PM
You've been a great help....


and keep well.