drain pipe slope

wetvent99 · May 22, 2008

Hello all,

I've been reading a lot about plumbing lately and have had difficulty finding the answer to this question: If fittings come in fixed angles (90, 45, etc), how can you create a 1/4" per foot slope on any given drain line? Assume we are working with PVC. I recently took a plumbing "class" and the instructor couldn't even answer the question.

Thanks for your help!

Gary Swart · May 22, 2008

There is enough flex in PVC pipe to get the required slope without fittings.

Sponsor · 2022-01-29T12:20:58-0800

Terry · May 22, 2008

Water fittings are at true 90's

Waste fittings have the 2% built in.

wetvent99 · May 22, 2008

Thanks for your help!

Jimbo · May 22, 2008

The devil is in the details, as they say. If you look a a plastic manufacturer's website, like Nibco or Charlotte Pipe, the give a lot of details, but especially they reference a long list of "comlies with" specs, like various ASTM standards. These are the standards which will give you the info on the angle built into tees, etc. Unfortunately, you have to pay for ASTM downloads, so I can't post one here.

Plastic is easy to deal with regardless. I never had to do cast iron work, but there you for sure had to have the angle on threaded tees, because there was no flex in the pipe. I assume on leaded joints it was pretty easy to set it where you needed it to be, but again, for many of us, that represents a lost art.

SRdenny · May 23, 2008

Jimbo
You have never worked with CI pipe? Don't you use no-hub on occasion? I hope for your sake that hj is in a good mood when he reads this thread.

Just for the record, no-hub pipe can be canted as much as 5%, according to the manufacturer's installation instructions. Also, no-hub fittings can be cut and ground using a chop saw or peanut grinder, but you didn't hear that from me.

Jimbo · May 23, 2008

Meaning I never installed a job in cast iron,or galvanized.. Cutting out old cast iron and replacing with ABS and a no-hub is easy enough.
hj is busy on another forum composing an answer to the guy who wants to boost the pressure in his propane tank to make a bigger flame in the fire pit.

hj · May 23, 2008

Pitch

The only fittings that "need" the slope built in are cast iron screwed drainage fittings. ALL other types can be moved in their hubs to make almost any slope you want within reason.

Markts30 · May 24, 2008

The old durham fittings used to have the built in slope as well...

hj · May 24, 2008

fittings

That is what cast iron drainage fittings were, although we used the term durham mainly for the larger pipe sizes.

SRdenny · May 26, 2008

Durham and steel waste and vent:
Positives:
Ridgid install, needs minimal strapping on vertical
Lends itself well to prefabrication
Negatives:
Low tolerance for error
Labor intensive, needs some muscle to install as well as some big wrenches
(can you say "cheater sleeve")
Dirty, greasy mule (threader)

dwpecksr · May 26, 2008

when laying pipe horizonally there is a 1/8 or 1/4 per ft sloap. when bringing it out of the ground on a slab I sometimes use a street 45 and then a 90 to make it straight in the vertical position. It makes for a better looking job.

hj · May 26, 2008

Durham

You missed one.
Hard to make that final quarter turn to line it up after a disgruntled employee, who is cutting and assembling fittings onto the cut pieces, has tightened the fitting to the point where it almost stalls the power drive.

(And there was no way I was going to give him the satisfaction of complaining about being "too diligent". Just listen to the sound of the power drive laboring, give him a smile, and grab the cheater pipe.)

dwpecksr · May 26, 2008

bsck in the days of galv pipe we would put a crooked thread on the pipe to get the sloap on the trap arm.

SRdenny · May 26, 2008

dw
Please don't take offense when I say, "Try using spell checker".

SRdenny · May 26, 2008

dwpecksr said:
when laying pipe horizonally there is a 1/8 or 1/4 per ft sloap. when bringing it out of the ground on a slab I sometimes use a street 45 and then a 90 to make it straight in the vertical position. It makes for a better looking job.

It also makes for one more bend where stuff can get trapped and lead to a stoppage. In the days of Durham plumbers used to roll fittings, the purpose of which was to use less of them, or so my father claimed. hj, what say you?

hj · May 26, 2008

fittings

We used the least fittings to make a good job, and we still do. One "rolled fitting" that was used frequently, and probably never by most modern plumbers was a 1/6 bend into a Y to make a rolling rise and horizontal connection to a lateral line. I wonder if those who do know how to make it can calculate the travel piece or if they cut and try till they get it right.

SRdenny · May 27, 2008

rolling offset is:
This works when the angle between your roll and rise is 45 degree

Roll(sq.) + Rise(sq.) + Run(sq.) = Travel(sq.)

If your angle is not equal to 45 degree the formula is 2 steps

rise(sq.) + run(sq.) = roll(sq.)

Then, Roll(sq.) + Rise(sq.) + Run(sq.) = Travel(sq.)

drain pipe slope

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