My drain line to the vent is pretty high/long ( had to avoid some other plumbing ).

How tall should the standpipe be?

Is there height requirements for the box itself?

Also, I have the option of taking the standpipe directly off of the trap, or weave it with 2 45-degree bends of the trap. Is one preferred over the other?

I was thinking the weaving over the trap would prevent the washer from flushing out and clearing the trap, no? However, doing that would force my standpipe to be smaller. Or, does the weave count as part of the standpipe height?

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  • So the vent is behind your finger ? Straight down is how it is usually done. I am concerned with the elbow to the left for a sink, It should be a sanitary tee, down to drain, up to vent. Same for the laundry, Ptrap into San-tee, down to drain, up to vent. There is code for distance to vent, Not sure but i think it is around 6 feet.
    – Alaska Man
    May 15, 2020 at 18:08
  • Here is a better picture: imgur.com/a/TFiKClh
    – Paul Knopf
    May 15, 2020 at 18:54
  • There is a good slope around the corner, and into the drain, for both the sink and washer.
    – Paul Knopf
    May 15, 2020 at 18:56
  • I know this is old, but the distances from trap weir to vent look too long for both those drains. 42” for 1 1/2”, 60” for 2”. Note that these are not local code dictated but physics dictated—it’s not possible to slope at 1/4” per ft and vent anything most distant. My suggestion is to vent straight up behind the sink. Drain lines can then join and move around that corner. The sink vent will act as the laundry vent.
    – snuggles
    Mar 4, 2023 at 12:28

1 Answer 1


Short Answer

International Plumbing Code: Not less than 18" but not greater than 42"

But it really depends on where you live, local codes, as well as the clothes washer manufacture.

Long Answer

Height Limit Factors:

  • The internal pump within the clothes washer needs to pump the discharged water vertically. It will have a limit as to how high it can pump. That is what limits the upper height.
  • Once the pumped water transitions from being forced by the pump to draining by gravity, depending on the GMP of the pump, there will be a backup of water as the water will drain slower by gavity. This limits the lower height.

Other Comments

You mention that the fixture drains have 'good slope' in one of your comments. Just be aware that there is a limit as to how much slope you can have on a pipe. The slope on a fixture drain cannot exceed that of the diameter of the pipe. Once you exceed the diameter of the pipe, the vent is cut off and the trap seal of the trap is no longer protected.

My local code limits the total change of direction on a fixture drain to 135° (the exception being toilets are allowed 225°). So here, the fixture drain for the clothes washer would pass as its total change is only 90°. However, the fixture drain for the sink would fail as it has a total change of direction of 180°. (This is my first time looking at the International Plumbing Code and I did not see this limitation during my quick skim, but it may be there, or somthing similar and I missed it.)

Regarding the termination of the clothes washer standpipe:

  • you can cut a hole in the wall to get to the top of the standpipe
  • you can rise verticaly in the wall and use one 45° near the top and come out of the wall on a 45°, or
  • use a manufactured laundry box

The benefit of a laundry box, in addition to a neat and clean installation, is that you can get one with water stops. Some locations may require by code that you have hammer arrestors on the water supplies to a clothes washer. Most laundry boxes come with the option to have them installed on the stops.

Relevent Excerpts from the International Plumbing Code



406.2 Waste connection. The waste from an automatic clothes washer shall discharge through an air break into a standpipe in accordance with Section 802.4 or into a laundry sink. The trap and fixture drain for an automatic clothes washer standpipe shall be not less than 2 inches (51 mm) in diameter. The fixture drain for the standpipe serving an auto- matic clothes washer shall connect to a 3-inch (76 mm) or larger diameter fixture branch or stack. Automatic clothes washers that discharge by gravity shall be permitted to drain to a waste receptor or an approved trench drain.




1002.1 Fixture traps. [...] The height of a clothes washer standpipe above a trap shall conform to Section 802.4.


802.4.3 Standpipes. Standpipes shall be individually trapped. Standpipes shall extend not less than 18 inches (457 mm) but not greater than 42 inches (1066 mm) above the trap weir. Access shall be provided to standpipes and drains for rodding.


FIXTURE DRAIN. The drain from the trap of a fixture to a junction with any other drain pipe.


909.2 Venting of fixture drains. The total fall in a fixture drain due to pipe slope shall not exceed the diameter of the fixture drain, nor shall the vent connection to a fixture drain, except for water closets, be below the weir of the trap.

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