I am running a 2 inch PVC kitchen sink drain that will be approx 35 feet long. I will only be able to get about a 3-3 1/2 inch drop on that entire run. Will this work? The only other option for me is to tie this sink drain into my washing machine gray water that drains into a separate fill line. I have very few options and very little room. I have gas lines in the way, heating and AC duct work in the way and floor joists in the way. Will this slope of 3-3 1/2 inches in 35 feet work?

The simple answer is yes. The only question is how long before it clogs up. As you likely know, 1/4 inch per foot is code for two inch pipe, and you are running at less than 1/8 inch per foot. If you have no other options, make sure to add easily accesible cleanouts to clear the drain if and when it clogs. I would suggest finding a way to get the proper slope (almost always a way, just sometimes it takes a lot of time and money), but I have been into some old homes and found sink drains and the like actually sloped backwards, and everything drained fine for years and years (definately don't ever do this). So once again, yes, it will work, but for how long, I couldn't tell you. Good luck and please let us know how things go.

I am going to have to try it. I have no other choice without moving duck work. Should I put in an auto-vent in the line and where should I put it?

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I will only be able to get about a 3-3 1/2 inch drop on that entire run. Will this work?

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Even at 1/8th" to the foot slope you would need a little over 4 1/4 inches and that's not enough for a kitchen drain line especially if you have a disposal installed.

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The only other option for me is to tie this sink drain into my washing machine gray water that drains into a separate fill line.

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If you're on a septic tank this is the only way to go. We route washer and kitchen drains through a grease trap before it ernters the septic tank.
Are you on a septic tank? Back to you, Tom

I am on a septic system, I do have a disposal and my washing machine does not go into the septic, it has a separate gray water fill line into the yard. I am going to take another hard look at my route and maybe I can get some more slope. You would not believe how tight it is under this 1922 house. It is going to be a "bear" getting this done.

I meant to say that I do NOT have a dsiposal.

I'm assuming that by saying,

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my washing machine does not go into the septic, it has a separate gray water fill line into the yard

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That your washer goers through a grease trap on its way to the septic tank.
If you wish to keep your drain field clear I'd tie the kitchen in with the washer. Can you notch joists to pick up more slope? Good luck, Tom

I found another way to run my sink drain, I tied it into a 2 inch cast iron drain that drains one of my bathroom sinks. I got a slope of about 9 inches in a 35 foot run. I put an auto vent under the kitchen sink and it drains well. If I fill the sink full and drain it, I can hear the vent suck a little air a few seconds after the sink gets empty. Oh, by the way my washer drain does not go into the septic tank at all, it drains into it's own fill line in the yard. We can get away with things like when you live out in a rual area. Thanks guys for your input.

Your washer runs to a grease trap where the grease and fibers are trapped before sending the liquid on to the septic tank. As a rule the kitchen and washerb are both run through the grease trap to remove grease, fiber and garbage before it can get out in the drainfield and clog up the holes that allow the liquid to percolate back into the soil. By bypassing the grease trap with the kitchen drain expect more drainfield problems on down the line. But if that's the only way to run the drain I wish you the best of luck. Tom

Hi bmgoldman,

Ive seen this setup before, where the washer runs outside the house and doesn't tie into septic(only when I had to tie it back into house sewer). But like you said, the things you can get away with in a rural or country setting.
Glad you found a way to get enough slope, its going to save you a lot of headaches in the future, good job. Thanks for the update, Take care.