# Drain Slope

I've heard 1/4" per foot and I've also heard 1/8" per foot is acceptable for waste lines. What is the ideal slope? Does it depend on pipe size or fixture type? (i.e. Toilet vs sink)

Thanks!

 afaroo Posts: 3,271, Reputation: 995 Ultra Member #11 Oct 8, 2008, 11:30 AM

Minimum 1/4" of fall per foot on 2" pipe or smaller.
Minimum 1/8" of fall per foot on 3" or larger.

1/2" per foot is Maximum.

The above is just an Info, Thanks.

John
 massplumber2008 Posts: 10,566, Reputation: 5097 Plumbing Expert #12 Oct 8, 2008, 02:52 PM

Hi John....

I believe you found the only exception to the rules I posted earlier.

MUST be IPC code...all others that I know of require as I posted...1/4" per foot 3" and smaller, 1/8" pitch per foot 4" and larger.

Always seems to be some exception to every rule! I swear!

I know I wouldn't go with only 1/8" pitch per foot on a 3" toilet line...just seems to be asking for trouble.

Have good day all...

MARK
 afaroo Posts: 3,271, Reputation: 995 Ultra Member #13 Oct 8, 2008, 02:54 PM
I agrre with you that's why I said an Info only, Thanks.

John
 fennecip Posts: 5, Reputation: 1 New Member #14 Jul 13, 2009, 03:41 PM
I too wanted to know the answer to this riddle of the "bubble". I took a 4' level and put it on a level surface, and elevated one end exactly 1 inch (1/4" a foot). It works out to 1/4 bubble, and with a 1/2 inch raise it "just cracked" the bubble (1/8" a foot).
 massplumber2008 Posts: 10,566, Reputation: 5097 Plumbing Expert #15 Jul 13, 2009, 04:43 PM

Hi Fenniecp:

If you want a 1/4" per foot of pipe and you are using a 4 foot level I believe it is easiest to tape a 1" piece of anything and read the 4 foot level as LEVEL each time you take a reading....then no guess work about where the bubble is...

Guarantees that 1/4" per foot every time (or 1/8" per foot if using 1/2" block on 4 foot level).

MARK
 fennecip Posts: 5, Reputation: 1 New Member #16 Jul 13, 2009, 04:52 PM
Oh I absolutely agree, or use a 6' 2x4 with a piece nailed to the end. I was just curious what it worked out to.
 speedball1 Posts: 27,686, Reputation: 9546 Senior Plumbing Expert #17 Jul 14, 2009, 06:09 AM

[quote] rickj
 downthedrain Posts: 1, Reputation: 10 Junior Member #18 Sep 21, 2010, 02:17 PM
If you have got a line of sight between your Point A and Point B you can run a string a line between the two using stakes. Run the line 1' above the grade to make sure discrepancies in grade do not interfere with the line. Use a spirit level to make sure the line is level between both points. Measure the starting height at Point A and the distance between the two points. For a 3" pipe multiply the distance between the points by 1/4" and for 4" pipe use 1/8" (check local building codes to see if they deviate from this standard). Use that sum to measure down from Point B, making sure to add the 12" for the line height).

Before backfilling make sure that the slope is uniform and even by using a spirit level. Take note of where the bubble sits and check for any points where the bubble is not sitting in the same position. Raise or lower these areas as needed. Take care that the underside of the pipe is sitting firmly on sand before backfilling.

Too little slope will leave waste sitting and building up in your pipe and too much flow could make the water separate from the waste (especially on 'watersaver' type toilets) and cause the same problem. (On non-city sewer systems: septic beds, etc. Too much pipe slope will increase the pressure on the tanks and force a higher flow rate then desired on your system).

All the best!
 speedball1 Posts: 27,686, Reputation: 9546 Senior Plumbing Expert #19 Sep 22, 2010, 07:17 AM
Mark nailed it! Pipes 2" and smaller = 1/4" to the foot while pipes 3" and up require only 1/8th per foot fall. I use a level and just crack the bubble on the big stuff and give it a little more for the 2" branches.
If I am held to zero slope I use a transit. Cheers, Tom

## Check out some similar questions!

I am hoping that someone can offer a suggestion to solve my problem. We recently purchased a 60 year old home. The sink in one of our bathrooms drains completely fine until the water has run for about 5 minutes and then all of a sudden it starts to back up and then drains very slowly. I have...

The slope [ 2 Answers ]

What is the slope of the line parallel to -2x-y=6?

Building a pre-slope for a shower pan [ 4 Answers ]

I used sand mix (with acrylic fortifier) for the pre-slope I built for a new shower pan. After the mortar sets up(two days later) I checked the surface by knocking on it with a stick, I heard hollow ring instead of solid thud in some spots. What does this mean? The material in the spots where I...

Undefined slope [ 2 Answers ]

If a line has an undefined slope, what can you say about the horizontal coordinates of each of the points on the line?

Washer drain line slope/heigth? [ 4 Answers ]

We have a 40 year old house in the country. Our washer drains into a 1 1/2" line through our home's back wall and underground for about 35 feet. Then the line runs out of the ground and out into the yard, terminating about 50 feet from the house, draining in the yard. Other older homes in our...