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newbie here. We live in a condo that is the third floor of a converted Victorian home (there are two units below us). We have in-unit laundry - a stacked high-efficiency washer and dryer (both front loading). It's in a closet that we would like to be our linen closet. We've got space off the kitchen where we would like to move the laundry. The problem is that the new location is far from the old drain pipes. It is near the kitchen sink/dishwasher drain pipes, though.

Can the high efficiency washing machine drain into the kitchen waste stack, which I believe is shared with our downstairs neighbors? Or Would we have to put in a whole new drain stack for the new washing machine location? That would make the whole project impossible as we would need to be running through our downstairs neighbors' walls.

We're located in Boston, MA if it makes a difference for code purposes.

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Firstly, disclaimers: I have no idea what rules might apply in the US, and I have also never heard of a "high efficiency" washing machine. I shall therefore answer from the point of view of practicality, and the assumption that "high efficiency" doesn't affect the water coming out of the washing machine's drain hose.

Size of particles: waste water from your washing machine presumably goes through a relatively small diameter hose. It therefore isn't going to have any problem going through your kitchen drainage stack (which should handle small pieces of food waste).

Type of water: waste water from your washing machine is going to have detergent in it. Just like water from your kitchen sink. I can't see any reason why the stacks would connect to different sewers, and therefore I can't see any reason why a national (US) or local (Boston) code would prohibit washing machine waste water from entering the same stack as kitchen waste water.

My experience: in the UK it is normal for a house to only have one drainage stack, which the bath water, toilet flush, kitchen sink and washing machine all discharge into.

In summary: I would find it very unlikely that you wouldn't be able/allowed to drain your washing machine into the kitchen stack.

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I'm not a plumber, but I have recently had our washer moved across our own house for similar reasons (in Colorado). Yes, barring some very strange plumbing setup, those pipes are all leading to outgoing sewage drains. Your plumber will need to assess the carrying capacity of that kitchen drain, as your washer dumps a lot of water rather quickly, and address possibility of back flow with that setup. Worst case the drain for the kitchen may need to be expanded or modified, but it should certainly be doable.

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Current plumbing codes, since 1985, require that a washing machine discharge into a 2" drain. The reason for this is that the volume of the water discharged at the high pressure of today's machines will cause the water to backflow out of the entrance to the drain. Also, you are required to provide an 18" vertical into the p-trap, draining the washer. Any remodels before this time period are highly unlikely to meet these requirements. Also, the kitchen sink does not provide an accessible p-trap for the washing machine, because it located in the kitchen cabinet, housing the sink. It is absolutely essential that you provide a p-trap to block the sewer gasses from flowing into your home. Any drain piping that you install for this washing machine must have an internal diameter of 2" and provide a minimum downward slope of 1/4" per foot away from the p-trap. The entrance to the drain must be above the height of the machine.

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    Welcome to Home Improvement. Are you able to provide a reference? Mar 14, 2023 at 19:40

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