45 degree slope of 3" waste pipe?

Sorry, No picture.

Twice this last week I saw horizontal 3" waste pipe dropped a foot or two over three to five feet span (with the use of 45 degree splices.) I have seen nothing in my library that says “don’t do it this way …” Although, because my material makes no exception to the to 1/4 - 1/8" rule I noted in these reports that elevation changes accomplished in this way will eventually cause problems and should be changed to 90 degree transitions. Am I correct?

Dennis, if you ever had to clean the line 45’s would allow a snake through without dismantling.

90’s are more likely to cause problems in drain line than 45’s. . .

Neither is improper.


Don’t see how this could cause a problem. I would far sooner see a couple of 45’s used in the manner you stated, than a 90. Better flow with lest restriction, and as mentioned in previous posts…much easier to snake/auger.

I think the problem generally comes from the fact that if you have too much slope, solids will build because the liquids drain too fast. However, if it’s over a short span, I do not think it will be a problem, especially if it drains into a vertical line. I would consider a three to five foot span a short distance.

Just my opinion, though, I haven’t spent much time in a drain line to see it happen.

Thanks guys.

Right now I am googling to see if I can find a definitive statement. The problem is that the charts and write-ups I use as reference do not sight exception to the 90 degree rule. Since I fear overlooking a problem with a seemingly correct situation I would like to see a research related report - so I am trying to find one.

I’d be guessing Dale has done the research .
Hands -on experiance. Thats what I’m talking about .:slight_smile:


Do you have the Code Check 4th Edition? On page 14 under drainage/changes of direction it states:

Vert to horiz or horiz to horiz through wye branches or 45 degree wy branches of fittings of equal sweep IRC 3005.1 UPC 706.3,4

Hope that helps.

I knew I’d read it some where, in Howard Massey’s Plumbers Handbook on page 25: Verticle offset in Drainage Pipes,“You can consider as straight any verticle stack with an offset of 45 degrees or less. Size it as a straight vertical stack…”

Just make sure the fittlings don’t reduce the diameter of the pipe or have any ridges that may cause an obstruction.

This is what I have.


UPC 706.4

706.4 Vertical drainage lines connecting with
horizontal drainage lines shall enter through fortyfive
(45) degree (0.79 rad) wye branches, combination
wye and one-eighth (1/8 bend branches, or other
approved fittings of equivalent sweep. Sixty (60)
degree (1.05 rad) branches or offsets may be used
only when installed in a true vertical position.


Thanks for the effort. Does the UPC distinguish between a Solid waste drain and a sink/basin drain? Is the “706.4” referring to a solid waste drain?


I have this picture too and is why I have a problem with contray statements. I did not find an exception with my google search but for some reason I could not get to the UPC - except to purchase. I may go the Library of Congress.
Thanks for the help.

Here’s a link to chapter 7 of the UPC


(If you want to see other chapters just change ch7 to whatever number you want.

Where are our plumbing guru’s? I’m not sure about the verticle drop in the horizontal drain lines using 45’s, but I think your statement “I noted in these reports that elevation changes accomplished in this way will eventually cause problems and should be changed to 90 degree transitions.” was pretty good, although I would have used “May” instead of “will” cause problems and wouldn’t have mentioned changing the fitting to 90 degree, I’d leave that up to a plumber


The link is helpful. FYI: 701.2.3 & 706.0. These do not provide exception to the 1/4" per foot to allow the use of the 45 degree connection with extention pipe piece to accomplish the elevation change. Yet, the old pro’s (mentioned above) have not noted problems with this type of junction. ??? Note that the section you provided above talks about the “stack” (a vent?) Most important, veridical is assumed not “out of plumb” and horizontal is assumed not “out of plumb” and connections to these span only the radius of the bend, i presume, and not the length of adjoining pipe. I presented the question to those at the ‘link.’ Again, Thanks.


The answer to your original post is here (apparently, 90’s are not allowed) if you are looking for a UPC reference.

706.3 Horizontal drainage lines connecting with other horizontal drainage lines shall enter through forty-five (45) degree (0.79 rad) wye branches, combination wye and one-eighth [1/8] bend branches, or other approved fittings of equivalent sweep.

As for the slopes in the pictures posted, these are just general references as to the “best” installation. In the codes, you will find a requirement for the minimum slope of a drain line, but there is no maximum (it can slope to vertical).

I didn’t read the entire thread, so I don’t know if this was already answered.


Thanks for coming back to this. My manuals contradict your comments so please stand by while I find these “manual” comments and post for you. This is not to challenge your intelligence but to help be get to the bottom of what I think I understand. Thanks again for your help.

You will find many references in manuals and other publications to contradict that statement, as I said, those will show the “preferred” method of installation - too much slope, problem - too little slope, problem.

My statement is with regard to the codes. There is no “maximum” slope for a drain line. It can be vertical (picture a wet vent).

Preferred methods and codes do not always go hand in hand.

I’m out the door for the day, I’ll check in while I’m sitting in traffic :smiley:

**Again, thanks to all as I have found the error of my ways **-
here is a lesson to be learned:

Waste Drain Slope:

  1. “2.2.2 INSIDE THE HOUSE
    Vertical Pipes Are Good Dumping the water into a vertical pipe (stack) is easy… The waste drops straight down and does not tend to get hung up anywhere.
    *** Sloped Pipes Are Tricky ***When the pipes aren’t vertical, life gets more complicated. We don’t want horizontal pipes because the waste would not flow. We certainly don’t want pipes with an uphill slope, because everything would collect at the low spot. Slope is usually ¼ to ½ inch per foot down away from the fixture. Maybe it would be better to have even more slope. Believe it or not, this is a bad idea. The solid and liquid waste will move nicely through the pipe with a ¼ t ½ inch slope, but if the slope is greater, the liquid will wash by quickly and the solids will get hung up on the bottom of the pipe. Once the slope becomes more dramatic, the solids and liquids will both move easily. Pipes with a 45-degree slope or more to the horizontal are considered vertical and called stacks.
    [THIS IS THE ANSWER TO MY QUESTION – “45-degree is considered a vertical pipe” and as such I was wrong to call this out to my client. However, not just any slope less than 45-degree is acceptable – as stated above and just below (or following).]
    They can carry solids and wastes effectively. … **Flow of waste in a drain system **Solid and liquid waste flows in vertical pipes much differently than it does in horizontal systems. In near horizontal pipes we talked about maintaining the slope of the pipe typically between ¼ to ½ inch per foot to have enough velocity to move the liquids and solids along the pipe, but not so much velocity that the liquids would pass the solids by and let the solids get hung up. …”
    [More is said here about gentle turns rather than abrupt direction changes. As I stated above that a 90-degree should have been used – well, I matched my mental image with the simplest statement that came to mind. That is to say, if I was to pick the proper transition connection from a box of fittings, I would have properly grabbed the “Waste Tee (or similar)” that accomplishes the 90-degree turn with an internal series of bends that at any tangent point would have a slope specified by the UPC. Again, the outward appearance of the fitting I described correctly but inappropriate and misleading for the conversation at hand.)]
    (Page 11/12 of Section Three - from the ASHI@HOME Training System “Plumbing” manual)

**This could be a resounding example of the tremendous benefit of the Bulletin Board. When level-headed, calculated dialog are maintained those of use who overlook, minimize, or simply forget a statement in our training can be brought back ‘on-base.’ As we cannot expect to be experts on all subjects it is essential to have this BB resource. Thank you one and all! :smiley: :smiley: :smiley: **