Garage Sink - It's a trap!

[HoosierBuddy]

Hey guys,

I replaced my garage utility sink earlier this week. After 13 years, the old one had disintegrated. I think the plastic sink became brittle with exposure to UV...in any case it had to go, so I got a newer, beefier utility sink and hopefully it will last longer.

I plumbed up the new one like I did the old one 13 years ago when we built the garage, but one thing is still bothering me.

The new sink included a p-trap which I installed under it, and connected it to the horizontal section of 1 1/2" drain pipe that goes through the exterior garage wall and enters a crawl space under the house (it's 3 steps up from my garage to my house). So, looking at that 1 1/2" drain as it runs downhill through the crawl space before connecting to the top of the 4" line...that 1 1/2" line has another trap in it about 6 feet after the p-trap I just installed under the sink. That trap is a "running trap".

In puzzling why that trap exists....I suddenly remembered that the 1 1/2" line was originally installed because we have a washing machine hook up (never has been used) in a closet adjacent to the garage.

So my questions:

1. Are running traps normally used for washing machine drain lines? That line starts in a wall in the laundry closet (currently is plugged) drops down and tees into the 1-1/2" drain I'm using for my sink about 4 feet before the running trap.

2. Should the fact I have a trap feeding a trap concern me? Will this eventually cause draining issues and clogs? There have been a few times in the past 13 years where I got a little "over zealous" in what went down that utility sink and it's gotten slow...but typically I can just allow the sink to fill, pull the plug and 12 inches of water pressure has been enough to push everything on down the line.

Thanks for any advice you can provide!

Phil

 

[Hilltopmasonry]

I am not a plumber so my advice probably is not good advice however I’m assuming you would not need a trap to feed into a trap but remember underneath the sink not only does a trap stop sewer gases from coming into the home it also serves as a catch to prevent stuff when it accidentally goes down the sink like a ring or something


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[Northislander]

The double trap causes drainage issues because air becomes trapped between the two traps and air is lighter than water. This causes the air to want to travel up as the water flows down resulting in NO DRAINAGE.

A vent allows the air to move instead of becoming trapped. This is why you vent a drain after the first trap if there is another trap or the potential of another trap.

This is also why you vent a drain after the first trap and before a common drain if you are connecting more than one drain. It helps prevent the possibility of a double trap and thus prevents a nasty backup.
So not a good idea to have to traps in series unless you have a vent in between

 

[59 wagon man]

some codes do not allow
1- running trap
2- multiple traps on a single line
3- maximum distance from trap to fixture
which you seem to have broken all 3 but I dont know the code where you live

 

[HoosierBuddy]

some codes do not allow
1- running trap
2- multiple traps on a single line
3- maximum distance from trap to fixture
which you seem to have broken all 3 but I dont know the code where you live

Well, 3 is not an issue, as the p-trap is under the sink.

How are washing machine drains normally trapped. Do they just use a p-trap as well?

If so, it seems like the fix would be to install a p-trap in the crawl for the washing machine drain and then cut out the running trap all together, replacing it with a short section of 1 1/2" straight pipe.

Phil

 

[Leaflessshadetree]

Was there a trap under your old sink?

If not is there any chance that it will freeze? It might be the reason someone did it that way.

 

[HoosierBuddy]

Was there a trap under your old sink?

If not is there any chance that it will freeze? It might be the reason someone did it that way.

Yes there was a trap.

The garage remains heated as the boiler for the hydronic heating is out there...so the trap should never freeze.

Phil

 

[LS6 Tommy]

Well, 3 is not an issue, as the p-trap is under the sink.

How are washing machine drains normally trapped. Do they just use a p-trap as well?

If so, it seems like the fix would be to install a p-trap in the crawl for the washing machine drain and then cut out the running trap all together, replacing it with a short section of 1 1/2" straight pipe.

Phil

None of your existing drain setup meets code for a washing machine drain. A washing machine drain is 2" minimum, with a trap 6"-8" from the floor and a standpipe 18"-30" up from the trap.

Tommy

 

[HoosierBuddy]

None of your existing drain setup meets code for a washing machine drain. A washing machine drain is 2" minimum, with a trap 6"-8" from the floor and a standpipe 18"-30" up from the trap.

Tommy

Good info. Thanks!

It may actually be 2-inches in the crawl. I was shining by flashlight at it from several feet away. I could have misidentified it.

Phil

 

[LS6 Tommy]

Good info. Thanks!

It may actually be 2-inches in the crawl. I was shining by flashlight at it from several feet away. I could have misidentified it.

Phil

You're welcome. I didn't mean to sound insulting.

Tommy

 

[JRC3]

Washing machine drain boxes do have traps inside the wall, but your's isn't like a typical washing machine drain.

My guess is someone did it in lieu of the above. What year was this done? Who did it, homeowner or pro?

It also could've been plumbed with the garage in mind...A trap in the garage would freeze...Hence the trap being in a warmer space. If it were me I'd leave it like it is and omit the sink trap.