Details about Washing Machine P Trap

[scavengerfilmstudios]

Currently building a laundry room off of the kitchen. The floor will be the same level as the main floor of the house, which has a basement.

My question concerns the P-Trap for the washer. I assume an S-trap isn't allowed, so I am planning on using a P-Trap. Once the water drains into the trap, I need it to go down so I can use a 90 degree elbow to go through the rim joist of the house. Once the water goes through the P-trap, does the pipe have to travel a required distance before it goes downwards? My very crude drawing has the section-in-question in red. My thoughts are that if it goes south right after the trap, it almost resembles an S-trap, though the horizontal area may negate that problem - just want to know if it has to go for any minimum distance first.

 

[MicEd69]

You sketch still shows an S-trap. You must have a vertical vent in the horizontal line within 5 feet (UPC) or 8 feet (IPC) before the line goes down. See below.

 

[TomFOhio]

You should tye your p-trap into a tee and then take the vent on up. What size pipe are you running

 

[scavengerfilmstudios]

I've decided to

You should tye your p-trap into a tee and then take the vent on up. What size pipe are you running

do the 'tee' on the horizontal pipe (the red part on my sketch). I have a choice of running 2" or 1 1/2" which is still allowed by the code in the township where this is. Not sure how I want to do that. There is enough room side-to-side to run either, but the 1 1/2" only goes a little bit in the basement before I can tie in, whereas the 2" needs to travel over 20'

 

[Geofd]

Use 2"" much less chance of it backing up in mass it must be 2"

 

[MicEd69]

I had assumed you were running a 2" line, and that is the distance from the P-trap to the vent dimensions of 5' and 8' in my response. And as Geofd indicated, 2" shoukld be used as that is what some codes now require. So even though 1 1/2" is allowed where you are, and many 1 1/2" washer drains exist and work fine, the codes were changed because many 1 1/2" drains proved problematic. As long as the vent is within the prescribed code distance from the P-trap, the additional distance the 2" has to run is not a problem.

The sketch also shows the fitting to use for the vent in the horizontal line is a Sanitary Tee, which is allowed in some codes and works just fine. However, some plumbers and some "over strict" inspectors interpret a Sanitary Tee on its back is not per their interpretation of the code. So, you may want to use a wye and 45° elbow Combo fitting for that vent connection.

Oh, if you do go forward with a 1 1/2" drain line, the vent needs to be within 3' 6" from the P-trap (UPC) or 6' (IPC).

 

[Twowaxhack]

Tee’s on their backs are installed by plumbers and inspectors who’ve never had any real experience cleaning drains or just simply don’t care and because the code allows it, they’ll install it.

Some codes will not allow it. If it is done then a cleanout should be installed to service it.

The only reason I could see using tees on their backs or side would be tight working spaces where making room for the proper fitting would weaken the structure, and in these cases a cleanout should be accessible to service the line.

 

[scavengerfilmstudios]

Tee’s on their backs are installed by plumbers and inspectors who’ve never had any real experience cleaning drains or just simply don’t care and because the code allows it, they’ll install it.

Some codes will not allow it. If it is done then a cleanout should be installed to service it.

The only reason I could see using tees on their backs or side would be tight working spaces where making room for the proper fitting would weaken the structure, and in these cases a cleanout should be accessible to service the line.

I would agree that a wye would be better than a tee, but if I go with 2" the space might be too tight. Also (and I certainly don't want to see argumentative, but is it 'more allowable' to use a tee as part of an air vent as opposed to a line with flowing water?

 

[Twowaxhack]

I would agree that a wye would be better than a tee, but if I go with 2" the space might be too tight. Also (and I certainly don't want to see argumentative, but is it 'more allowable' to use a tee as part of an air vent as opposed to a line with flowing water?

If it’s 6” above or below the overflow of a fixture then I pipe it as a drain…….not a vent.

This is because of the possibility of the line filling up with sewage. This sludge can clog that tee on its back.

I’ve seen it myself several times so I know it does happen.

But carry on, it’s your choice, not mine.

 

[MicEd69]

I would agree that a wye would be better than a tee, but if I go with 2" the space might be too tight. Also (and I certainly don't want to see argumentative, but is it 'more allowable' to use a tee as part of an air vent as opposed to a line with flowing water?

As some codes allow sanitary tees on their back for vent connections, I would say yes, it would be "more allowable" for using them as vents as they do provide issues if used for flowing drainage. And depending on your piping layout, there could be no difference at all between using a sanitary tee or a combo fitting for a vent.

For instance, I added a sink that connected to the stack above all other drains. It was too far away from the stack to use it as the vent, so I used a sanitary tee on its back on the drain line to the stack. I took that vent line up into the attic and connected it to the stack. There was no way that vent line would fill with sewage, so either fitting would result in providing a proper functioning vent.

Now, for all drainage and vent piping, you do need to be diligent about providing cleanouts for your particular piping layout. You need to review the layout and provide a cleanout wherever required for future maintenance issues.

 

[TomFOhio]

I've decided to

do the 'tee' on the horizontal pipe (the red part on my sketch). I have a choice of running 2" or 1 1/2" which is still allowed by the code in the township where this is. Not sure how I want to do that. There is enough room side-to-side to run either, but the 1 1/2" only goes a little bit in the basement before I can tie in, whereas the 2" needs to travel over 20'

The tee should be in the verticle line of your drawing. Not where the red line is.

 

[scavengerfilmstudios]

The tee should be in the verticle line of your drawing. Not where the red line is.

Not looking at my sketch, but are you saying that the graphic from Stack Exchange (attached in the first reply) is incorrect?

 

[MicEd69]

Not looking at my sketch, but are you saying that the graphic from Stack Exchange (attached in the first reply) is incorrect?

You can install the vent as shown below, but the trap arm distance cannot be more than 5' (UPC) or 8' (IPC), assuming you are running a 2" line. If you have to go farther than those distances, the vent HAS to be installed in the horizontal as shown in the Stack Exchange sketch above. And if the layout of the piping works best to have the vent in the horizontal line, that is just fine. So, saying the vent line "should be in the vertical line" is not actually factual.