I have a long copper drain pipe that runs nearly horizontally 8" above the floor for the length of my basement. At the high end, a utility sink connects in. A couple feet downstream on the horizontal pipe, the vertical kitchen drain connects in from above.
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The utility sink drain very slowly. When I opened it up, I found it clogged with gunk including white powder, which I assume is dishwasher soap.
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I removed as much of the debris as I could see and installed a new P trap, but the drain is still quite slow.
The utility sink drain trap is below this long horizontal drain pipe. So, I'm wondering if the upstairs kitchen sink and dishwasher debris are flowing the wrong way on this horizontal pipe sometimes and clogging the utility sink drain. Is it a bad system design? Should the utility sink trap be higher than the main horizontal drain pipe run?
Thanks for your thoughts.

You still have gunk in your waste drain. It appears that you have done your best to remove it without success. Now its time for a Pro. A Licensed Plumber, with the proper equipment and the knowledge to use it.

Best Wishes

Thank you for the reply.
I'm still curious: Is it bad that the utility drain trap (shown in the first picture) is below the level of the main drain line? Or is that normal? I'll try snaking the line myself and flushing it out with a strong hose spray. I'll let you know how it turns out. If I still can't get it, I'll call a pro. Thanks again for the help.

The trap is suppose to be that way. The problem with the utility drain is there's no legal vent. It's using the 2nd floor kitchen drain as a wet vent(not code allowed).

Thank you. That's good to know that the drain is supposed to be that way!
As for the vent, it may have one. Here's a picture:
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You can see the vertical drain pipe that comes down from the kitchen upstairs.
Branching off on the left side of it is a trap that is open at the top.
I've been wondering how that works, because it seems to me that that trap would generally stay dry, so sewer gases might escape into my basement. I'm still trying to understand it. (I'm just reading up on drain vents now that you've brought it to my attention.)
BTW, the utility sink the basement seems to fill up with soap suds every day, even when I haven't run the washing machine. It must be soap from washing the dishes in the kitchen. So, I guess that reinforces the theory that the horizontal basement drain line is clogged and the waste water is backing up into the utility sink drain.
Thanks again for your insights!



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Thank you, Steve. You're right; there's no vent at all for the utility sink. :-( What I pointed out in the follow up picture, I now realize is not a vent at all, as it doesn't go up and out of the house. I think it's probably left over from what a previous person used as a laundry drain. Now that it's unused, it should probably be capped to prevent sewer gas from entering the house, right?

I think a big problem with my set up is the drain slope. Over 30 feet, the main basement drain line drops only a couple of inches. It should drop at least 8. I'll have to lift one end of it, which will be a big project. Then I'll have to snake it to remove years of debris build up, as discussed.

Thanks again.

In addition to the lack of venting and the lack of downslope in my main basement drain line, it appears that all the vertical drain lines from upstairs join the main horizontal drain line in the basement with medium-sweep san tees. That's no good, right? Isn't a vertical drain supposed to join a horizontal drain using a wye or a long-sweep tee?
So, now I'm looking at adding vents, inclining the pipe to at least 1/4" per foot, replacing the medium-sweep san tees with long-sweep tees, and snaking the line to remove years of build-up (which should be easy since I'll be cutting the pipe in many places). Does that sound reasonable?

Sounds good to me. Yes, the tees should be combos(long turn tee or tee/wye different names for the same fitting).

Thanks, Steve!