Can the J bend in a p-trap be installed "backwards"??? J-Bend Lo Inlet

Users who are viewing this thread

zbdd2

New Member
Messages
2
Reaction score
0
Points
0
Location
Tennessee
I am hooking up the drain lines under a relatively deep bowl sink. The installation includes a garbage disposal. In order to get the J-bend of the p-trap to meet the arm of the trap, I have to attach the long side of the J to the arm and the T that combines the disposer and the second bowl to the short side of the J. This is backwards to me but seems like it should work. Will it? Am I creating other problems?
 

Terry Love

Plumber
Messages
42
Reaction score
1
Points
8
Location
Bothell, WA
Website
terrylove.com
It will work, it can raise the water level in the disposer though.

Many kitchen remodels should have the drain at the wall lowered 3" if you are using a deep bowl kitchen sink.

The last kitchen remodel I worked on, the contractor was going to just flip the p-trap.
It would have left some water in the disposer all the time, if I hadn't caught it for the homeowner before the cabinets were installed.

sink_dw.jpg


j_bend_low_inlet.jpg
 
Last edited by a moderator:

zbdd2

New Member
Messages
2
Reaction score
0
Points
0
Location
Tennessee
Lowering the rough in would have been the best thing to do but we had no idea what kitchen sink we would be using when that part of the project was done and the difference in the rough in never occurred to me. Disposer installation is new to me as well as how those affects things. The house was all but gutted and all of the galvanized supply and all of the cast iron dwv lines except for one run in a concrete slab were replaced. This is the last fixture that I have to finish the plumbing on and I feel fortunate that this is the biggest issue that I have come across. Live and learn.....

Thanks for the info........
 
Last edited:

hj

Master Plumber
Messages
33,602
Reaction score
1,040
Points
113
Location
Cave Creek, Arizona
Website
www.terrylove.com
trap

Doing it will not change the level of the water in the disposer, as long as the pipe in the wall is not above the disposer's outlet. IF it is you MUST lower the pipe or you will have constant problems, not the least of which will be premature rusting of the disposer. One problem you will have is that the "outlet" of the trap has a very shallow insertion for the tailpiece so it will fall apart very easily if bumped or vibrated.
 

Redwood

Master Plumber
Messages
7,335
Reaction score
13
Points
0
Location
Connecticut
Even Watts made this mistake on their website product pictures... :eek:

503333PB.jpg


Problem is like HJ said they fall apart easy and leak...
 
Last edited by a moderator:

Terry

The Plumbing Wizard
Staff member
Messages
29,942
Reaction score
3,458
Points
113
Location
Bothell, Washington
Website
terrylove.com
If I know there are going to be new cabinets, the first thing I check is drain height. Almost all new remodels are going with deep sinks.
And that means lowering the drain while you have access to to the wall behind the cabinets.

reverse-p-trap-install.jpg


Here is a reverse trap installation.
 
Last edited:

Terry

The Plumbing Wizard
Staff member
Messages
29,942
Reaction score
3,458
Points
113
Location
Bothell, Washington
Website
terrylove.com
They do make a low-inlet J bend

p-trap_too_high.jpg


A standard trap with a bowl that is too low for the trap arm.


j_bend_low_inlet.jpg


J Bend with low inlet
http://www.keeneymfg.com/

j_bend_low_inlet_installed.jpg


J bend with low inlet, installed.
They make these for 1-1/4" and for 1-1/2"

kohler_caxton_installed.jpg


Putting a granite counter top on a 30" cabinet and undermountng a Kohler Caxton bowl pushed the drain a bit lower. The lo-inlet J-bend fixed that.
 
Last edited:

Terry

The Plumbing Wizard
Staff member
Messages
29,942
Reaction score
3,458
Points
113
Location
Bothell, Washington
Website
terrylove.com
Here is a reversible p-trap that works!

p-trap_reverse_dearborn.jpg


Dearborn makes a p-trap with a J Bend that can be reversed.

Dearborn Brass P9703W
 
Last edited:

Sydflash

Member
Messages
44
Reaction score
0
Points
6
Location
MA
This thread was helpful, but I want to make sure that I understand.

There is no harm in reversing the "J" bend for a "P" trap, correct?

I am trying to install an offset in my kitchen sink drain to prevent the dishwasher and the waste water from the R.O. filter from audibly trickling into the trapped water.

This is what I have roughed in:

IMG_0015.jpg
IMG_0016.jpg


I think what worries me is that the lower nut on the "J" will always have water above it.
 

Reach4

Well-Known Member
Messages
38,797
Reaction score
4,412
Points
113
Location
IL
sydflash, you have a couple of problems. One is that you have what is called an "S trap". I suggest you search out that term.
 

Terry

The Plumbing Wizard
Staff member
Messages
29,942
Reaction score
3,458
Points
113
Location
Bothell, Washington
Website
terrylove.com
Sydflash,
You can install a santee with an AAV for venting there, and air straight at the drain. That would fix the p-trap situation too.
 

Sydflash

Member
Messages
44
Reaction score
0
Points
6
Location
MA
It's actually an unusual set up with a wye in the basement:

IMG_0017.jpg

No idea why they did it this way, but the branch to the left is a dedicated vent for the sink, with the other branch being the drain. The vent is only a vent and no other fixture uses it as a drain. You can't see it but the branch to the left goes to the wall in that bay and then up.

I wouldn't have done it this way myself, but I think this is a proper vent. The sink never gurgles even if I fill it with water.

TAt one time it exited the roof on its own, but it was the front of the house. So, when I added an addition, I tied it into the stack near the roof in the back.

Will I still have the syphoning problem of "S" Traps with this vent?
 
Last edited:

Jadnashua

Retired Defense Industry Engineer xxx
Messages
32,770
Reaction score
1,190
Points
113
Location
New England
The problem with an S-trap is that they can drain TOO well and won't leave enough water in the trap to maintain the seal all of the time. A proper vent must come off of the trap arm before it starts to go down and within specified distances based on the pipe diameter used. This will cause the siphon to break before the trap can be evacuated enough to cause problems.
 

Sydflash

Member
Messages
44
Reaction score
0
Points
6
Location
MA
Also, it's probably not clear in the pic that there is six inches of pipe between the bends before it goes through the floor - the part with the purple cement on it. Is 2 x the diameter of the pipe still the standard?
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks