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Discussion Starter · #1 ·
Hello there, everyone!

I'm installing the drain for the washing machine and wondering if I need to vent it or whether the main vent stack is sufficient for my needs.

In this diagram, you can see that the main 3" drain runs directly under the washing machine drain. It will simply drop down the exterior wall, have a P trap (minor pitch, at least 4" between trap and elbow continuing down) to the 3" drain pipe. At the end of the 3" pipe is a vent stack that comes up through the home space into the attic, where it runs back through the attic space, following the drain until it exits the roof about the same point as the drain below goes to the septic.

The other drains on this line are not vented and it seems to me that this wouldn't need to be either but I thought I should ask before committing. Do I need to add a vent to this drain or will the master vent at the end of the line be sufficient?

Thanks for your time!

 

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When your washing machine empties it is usually under pressure from the pump, not just vented, and could pressurize your main vent, so you may not want the trap near the top of the washer drain pipe, This looks like it might be an older house before the 80's?
 

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Discussion Starter · #5 ·
When your washing machine empties it is usually under pressure from the pump, not just vented, and could pressurize your main vent, so you may not want the trap near the top of the washer drain pipe, This looks like it might be an older house before the 80's?
Hi there guys and thanks very much for the help. I was hoping to get some pics of the vent system in the attic space to explain a bit better but it's so compact and cluttered with duct, it's really impossible to give you guys any idea of what I'm working with. I'll try to explain and provide another schematic of sorts to explain.

Basically, it's as simple a system as you can get. The 3" drain runs along the side of the structure(30 feet) and a kitchen sink, dishwasher, washing machine, shower, br sink and toilet connect to it along that wall and in that order. At the higher side of that 3" pipe, it has an elbow that runs it vertically along the corner of the house and into the attic where it elbows again, with what is now the vent stack running back through the attic space right above the 3" drain pipe, exiting at the other corner of the attic space through the roof. If I needed to, I could run the washer vent through the cap of the wall and tie into the 3" vent pipe at about the midway of the entire run in the attic space.

In this setup, the shower, br sink and toilet are the connections that are upstream of the washing machine, if this is a necessary consideration.

This is a sideview of the plumbing run. It's just a simple run down one wall with all but the kitchen sink directly above the 3" drain. I've placed a mechanical drain at the kitchen sink already.

Rectangle Font Red Parallel Slope
 

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My AHJ will allow 6' and still be legal to a vent. A lot of water goes out of a washer at times.
Will your local area allow you to use the washer as grey water and use it for watering plants/grass? That is what I did for my washer.
 

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Discussion Starter · #9 ·
Hey there guys, I'm finally back to this bit of construction. Would this combination of fixtures meet the needs and code compliance of a washer drain?

 

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Dish or clothes? Dish fine, clothes, have a cycle (mine does) where it back flushes the filter scree for each wash. All those particles could clog up your concept.
Why cant you use a P trap and extend the horizontal pipe.

2" is not a great vent, Clothes washer spit out a lot of water all at once. Venting is very important with large volumes of water.
 

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Discussion Starter · #11 ·
Sorry if not clear, this is for a clothes washing machine.

1) What would be the difference between a p trap and what I've got?

2) Why do I need a longer horizontal? I only have two stud bays to work in and I've already swept the washer box to the left as far as I could.

3) As for the 2" vent, it ties into a 3 above in the attic space. I've never had an issue with a 2' run in this manner. Out of a few homes and many washing machines, all have had a 2" vent at this point.

Thanks for your time!
 

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Sorry if not clear, this is for a clothes washing machine.

1) What would be the difference between a p trap and what I've got?

2) Why do I need a longer horizontal? I only have two stud bays to work in and I've already swept the washer box to the left as far as I could.

3) As for the 2" vent, it ties into a 3 above in the attic space. I've never had an issue with a 2' run in this manner. Out of a few homes and many washing machines, all have had a 2" vent at this point.

Thanks for your time!
Looks fine to me.....not sure what's up with the other posters....
 

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Discussion Starter · #17 ·
I think you need a longer stand pipe. Lower trap and up a little higher for the pump.

Let's see what the masters say.
Thanks very much, I couldn't find anything regarding minimum stand pipe, I found min 24" drain height for top load washer and 30" for front load but didn't find anything regarding stand pipe length.
 
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