Clear pipe mystery: sink won't drain

April 22, 2005 6:54 AM

My kitchen sink is very slow to drain. The pipes are clear and the garbage disposal is new. When I run the disposal, all the water/other stuff in the sink drains out without too much trouble. Is there some way to adjust the spinning element in the disposal to make sure the drain holes inside it are fully open?

Yesterday I ran the dishwasher before leaving for work and when I returned home in the evening, the sink was full of the dishwasher water. I flipped on the disposal and in seconds all the water drained. So far, I've done several things to try and fix this problem:

• Install an air-gap to prevent water from draining back into the dishwasher.
  
• Un-hook the disposal and check the pipes (they're clear)
  
• Run hot water through the disposal
  
• Run ice cubes through the disposal
  
• Try turning the internal mechanism with the alan wrench provided (that was just basically manual operation)
  
• Look indies the 'mouth' of the disposal and the 'throat' type area that leads to the exit-pipe. Seems pretty clear. No greasy build-up or anything.
  
• Remove and reattach the exit-pipe from the disposal (also clear)

posted by clgregor to home & garden (12 comments total)

Here's a model of a garbage disposal. I'm thinking maybe the "shreeder plate" is where my problem is. I tried to put this link in the original posting but screwed up something there.
posted by clgregor at 7:11 AM on April 22, 2005

I think you are correct in your determination that the clog is in the disposal itself, not the associated piping. Two possible causes come to mind: silt and grease. Silt would come from not running enough water when you run the disposal and not running water for a period after the grinding is complete. Once you ran the disposal with the dishwasher water it probably cleaned out any silt, but a new load of silt can form the next time you use the disposal. If it is grease it could be built up in areas inside the disposal that you can't easily see. When you say you used hot water, did you use boiling water? That with some soap is a good way to get rid of grease. I have never put anything like Draino gel down a disposal, but I think these products are designed for such use.
posted by caddis at 7:27 AM on April 22, 2005

Has this always been this way? It's possible that there is insufficient slope from your disposal to the house's main sewer pipe. If this is true, the disposal is acting as a pump, pushing the water further down the drain plumbing to the main sewer pipe in the house.
posted by kc0dxh at 7:52 AM on April 22, 2005

Caddis, I still get a backup even after running all that water from the dishwasher through the disposal. So i don't know if it is silt. And the disposal is so new, I am fairly certain it isn't grease, but I didn't use boiling water, yet.

kc, I have heard Drano is bad for disposals. This pipe angle thing might be a factor because after the "U" shaped part of the pipe the pipe seems to go straight back, not down. This 'pump' thing might have something to do with it, unfortunately.
posted by clgregor at 8:08 AM on April 22, 2005

You might try installing a $5 one-way valve on a T just below the sink to allow air into the line (water won't get out). Imagine how water would flow much more easily out of an inverted bottle if you punched a hole in the bottom.
posted by weapons-grade pandemonium at 8:16 AM on April 22, 2005

If you've always had this problem, I'd suggest exploring how the sink vents. If the vent is undersized or non-existent then this could explain the problem.
posted by jbradley at 8:18 AM on April 22, 2005

If the vent is undersized or non-existent...
Or too far away. The vent has to be reasonably close to the sink to be effective. That's why I suggested the valve. Perhaps the new disposal has restricted the drain opening so air cannot replace the draining water fast enough. Might not have anything to do with a clog.
posted by weapons-grade pandemonium at 8:26 AM on April 22, 2005

I'll third the venting suggestion. Was the new sink put in professionally? Our landlords built the bathroom in our apartment and didn't vent the sanitary line. As a result, our toilet trap is sucked dry on every flush!
posted by Popular Ethics at 8:57 AM on April 22, 2005

I think venting may be it, they installed a new sink, dishwasher, disposal before I moved in, and there were other shoddy installation glitches...the dishwasher drain hose was attached to the disposal without punching out the drain hole in the disposal....some wiring in other areas was mixed up. Are there any good sites to look at venting diagrams/instructions/explanations?
posted by clgregor at 11:41 AM on April 22, 2005

My bet is that your disposal is fine and the pipes are draining slowly. Slow pipes might be from a bogus vent but I can't imagine that your dishwasher water would pool in the sink and sit there all day unless there was some blockage.

To verify the disposal is okay I'd just take it out. Most of them pop out surprisingly easily, especially when new. Disconnect the electrical first. When it's out you'll be able to see right through it and verify there's no plug.

Beyond that, I'd call a plumber and explain the problem. They'll probably run a snake down the pipes and everything will be fine. If you don't know a good plumber Roto-Rooter is usually a good bet.
posted by deanj at 4:45 PM on April 22, 2005

The device you may need is called an AAV, or Air Admittance Valve. There are brand names, like Studor Vent, etc. Check the building codes to see if you can install one.
posted by weapons-grade pandemonium at 5:00 PM on April 22, 2005

Turns out it just needed draino. The maintenance guy fixed it in about two seconds. There I go thinking more complex than I needed to again!
posted by clgregor at 10:19 AM on April 30, 2005