Do I really need .25 inch slope for drain?

[Nate848]

Hello

I am roughing in a drain in new construction and its about a 38 foot run of 2" pipe just for the laundry room washer and sink in the laundry room. I only can get about 4 inches of pitch/slope in the run. Do you think only have a .1/8th or .15 inch per foot of pitch is ok for a 2" pipe? I dumped a cup of water in and it drained fine but code says I need .25 per foot.

Thanks

 

[UFGator121222]

1/8” will work fine. Especially if it’s only grey water.

 

[Diehard]

The code says 1/4"/ft for a reason.
It may work fine for a while but the slower average velocities tend to cause build up and eventual blockage sooner.
Why not use 3"?

EDIT: Also keep in mind that you are sizing a drain pipe for a Laundry Room not a cup of water.

 

[UFGator121222]

Again 1/8” will work just fine. Why use 3” when there is absolutely no need to and that doesn’t change the fall at all. You will have absolutely no problem with 2” and 1/8 of fall. Everyone does it if it is needed. Your washer had a pump that will be pumping water out also. 2” pvc can handle something like 21 fixture units and you are using about 5 fixture units so no don’t use 3” that makes absolutely zero sense. You will have no issues at all with 1/8” 2” pvc. Good luck with it and don’t sweat it because you had it right the whole time.

 

[voletl]

Actually having 3 inch pipe does change the fall 3 inch pipe you can pitch at 1/8 per foot by code I'll send you a link to a code book maybe you should read up on it

https://up.codes/viewer/colorado/ipc-2015/chapter/7/sanitary-drainage#7

2 inch pipe will have quarter inch per foot fall.

 

[Diehard]

Again 1/8” will work just fine. Why use 3” when there is absolutely no need to and that doesn’t change the fall at all. You will have absolutely no problem with 2” and 1/8 of fall. Everyone does it if it is needed. Your washer had a pump that will be pumping water out also. 2” pvc can handle something like 21 fixture units and you are using about 5 fixture units so no don’t use 3” that makes absolutely zero sense. You will have no issues at all with 1/8” 2” pvc. Good luck with it and don’t sweat it because you had it right the whole time.

The 21 fixture units you mention is for a 1/4" slope, not an 1/8" slope.

In my mind there are plenty of reasons to use 3".
1. It's required by the applicable plumbing code.
2. It reduces the fall by 50%.
3. Many large new washing machines can and do exceed the flow capabilities of the standard 2" systems.

I wouldn't use the 2" even if there was sufficient room to install it at 1/4" slope.

 

[CT18]

Some codes say washer boxes have to discharge into a 3" stack. Also make sure it is vented correctly.

 

[frodo]

Nate,
If it were me, I would run a 3'' line horizontally at 1/8'' per foot
turn up with a 3'' 90 degree bend.

install a 3x2 bushing inside the 3'' 90

come up vertical with a 2'' pipe

the 2'' will fit inside your wall,

 

[Nate848]

thanks for the replies everyone

Nate,
If it were me, I would run a 3'' line horizontally at 1/8'' per foot
turn up with a 3'' 90 degree bend.

install a 3x2 bushing inside the 3'' 90

come up vertical with a 2'' pipe

the 2'' will fit inside your wall,

thanks for the advice and everyone else.

 

[Diehard]

I would not rely on an AAV(Air Admittance Valve) for a washing machine due to the potentially high discharge rates.

 

[chiraldude]

Not sure I agree with the statement of high discharge rates. The last 3 washers I have owned were high efficiency units that never dumped more than 3 gallons at a time into the drain. The drain pumps were tiny and discharge was through a 1" tube.
Can you even buy an 20th century type washer that dumps 20-30 gallons into the drain in less than a minute?

As for the pipe, make sure you put in a cleanout in a spot that is easy to find and access. Also be meticulous about deburring cut ends. Lint will tend to collect on sharp edges.

 

[frodo]

Whirlpool pumps at 15 gpm with the stand pipe at 30'' off the floor
for each 12'' added to the stand pipe the gpm pumped rate is diminished by 1 gallon per minute

 

[Diehard]

GE also states 15 gpm with a change of 1 gpm for every foot change.

I am not basing the high flow rate POTENTIAL on my experience. I have a 30 year old Maytag. I am basing it on the numerous articles and peoples experiences.

Apparently 12 to 17 gpm is not uncommon on some of the newer large machines.

Here's one example on the subject...
https://www.pmmag.com/articles/85477-it-s-not-the-plumbing

 

[chiraldude]

I saw that article too but then I noticed it is dated June 8 2000
Maybe it is true but I remember the washing machine my parents had in the 70' that discharged 20+ gallons at a time out of a 1 1/2" tube.

 

[Diehard]

Yeah but of course the tube size doesn't represent the total gpm.(Are you sure the ID was 1 1/2"?)
Would have to assume the newer high capacity, high discharge rates, going through a 1" hose, is at a slightly higher pressure.

EDIT: I just looked at my hoses. I do notice that he newer ones have a much thinner wall but I don't think the hoses from the 70,s were 1 1/2". How did they get them in a standpipe?

EDIT2: Just looked at the ID of my newest of the 2 hoses I have connected to each other. It has a 7/8" ID. I see on the web that some are showing 5/8" ID washing machine hoses.

 

[frodo]

As for the pipe, make sure you put in a cleanout in a spot that is easy to find and access. Also be meticulous about deburring cut ends. Lint will tend to collect on sharp edges.

just my opinion based on years of experience

if the washer is on a first floor outside wall, you stick the c.o out the exterior wall at 18''
same height as the sewer machine.

if it is on an interior wall. you install the clean out behind the washer/ dryer at a height of 48''

you make the size of the clean out 2'' as per code