Plumbing: P-trap or vent needed on drain pipe for RO/DI waste line?

[OlafsReef]

Need advice on plumbing the waste line to the drain pipe for my RO/DI.

I am building a mixing station and running input and waste tubing lines to unused water lines I found inside a cabinet in our laundry room (I assume for an old utility sink). Right now the drain is just an uncapped 1.5" pipe sticking out of the wall. Do I need to install a p-trap onto the drain line in order to prevent sewer gases from venting out when waste water runs down there, or can I just toss the waste line down the open drain pipe?

Googled around a good deal and still not certain as I see laundry machine drain lines directly feeding into drain pipes. Any guidance is appreciated.

 

[lapin]

I would cap it. Drill a hole for the RODI waste line and shove it way in there.

 

[Joe31415]

YES!!!!
In fact, rubberband a plastic bag over that stub in the mean time. That 'smell' you probably notice when you're near it is sewer gas coming back up.
Get a few parts from Home Depot to make a P trap and you'll be good. Just make sure the discharge line from the RODI system stops on this side of the trap. If you shove it all the way through, the discharge water won't keep the trap full and once the water in there evaporates, it won't trap the gasses anymore.

As far as it not being needed on a washing machine, there should be one on there as well. Some people may rely on the water that's sitting in the bottom of the machine between uses, but that wouldn't be up to code. It's also common for people to directly connect a dishwasher or washing machine discharge to the drain under their sink. When they do that, it needs to be on the sink side of the trap. Doing it on the other side opens up the drain to the interior of the house. This would especially be a problem with a dishwasher since the vacuum breaker/anti siphon device (the thing up on top of your sink) would let the gasses right in to your living area.

In short, yes, you absolutely need that drain trapped.

 

[OlafsReef]

YES!!!!
In fact, rubberband a plastic bag over that stub in the mean time. That 'smell' you probably notice when you're near it is sewer gas coming back up.
Get a few parts from Home Depot to make a P trap and you'll be good. Just make sure the discharge line from the RODI system stops on this side of the trap. If you shove it all the way through, the discharge water won't keep the trap full and once the water in there evaporates, it won't trap the gasses anymore.

As far as it not being needed on a washing machine, there should be one on there as well. Some people may rely on the water that's sitting in the bottom of the machine between uses, but that wouldn't be up to code. It's also common for people to directly connect a dishwasher or washing machine discharge to the drain under their sink. When they do that, it needs to be on the sink side of the trap. Doing it on the other side opens up the drain to the interior of the house. This would especially be a problem with a dishwasher since the vacuum breaker/anti siphon device (the thing up on top of your sink) would let the gasses right in to your living area.

In short, yes, you absolutely need that drain trapped.

Perfect, thanks for the input Joe.

 

[SteveMM62Reef]

I would go ahead and install a Laundry Sink. They are great for Cleaning Aquarium Equipment. I don’t think I could live without mine. Also I have a post, with a Quarter turn Valve for my RO/DI, mounted on the Sink Deck. I attached my RO/DI waste tube to the side of the valve, with a couple of Wire Mount Straps, directed to the sink, so I can monitor the waste water flow.