Is it normal for a garbage disposal to spit stuff up on other side?

February 19, 2020 10:13 PM

Pretty self-explanatory, I think. Sometimes when I turn my on garbage disposal, the drain on the other side of the sink erupts. what's causing it? Could it be something isn't working right on the disposal?
posted by BadgerDoctor to Home & Garden (8 answers total)

The garbage disposal outlet and the drain line for the other sink probably join together at a t-connector above a sink trap. The symptom you describe is usually an indication of a minor obstruction (perhaps grease buildup) in the t-connector or immediately downstream (such as the line leading from the t-connector to the trap, or in the trap itself). The obstruction is not sufficient to prevent the disposal or other sink from draining, but sometimes when the disposal is turned on its initial output is greater than can be quickly passed through the t-connector (or somewhere downstream), which causes the water to briefly backup above the t-connector through the other sink's drain line and up into the other sink.
posted by RichardP at 10:27 PM on February 19, 2020 [3 favorites]

One thing you could try that might fix this is using the garbage disposal's apparent tendency to pressurize your drain line to blast the obstruction out of the way. Fill both sinks with very hot water, hold a plunger over the drain line in the erupting sink, pull the plug on the disposal side, switch on the disposal and see what happens.
posted by flabdablet at 11:46 PM on February 19, 2020

If that doesn't work, next step would be to wait for both sinks to empty, then sit an empty bucket under the U bend, unscrew the inspection plug on the bottom of the bend, and use a bendy wire hook to pull a plug of nameless urk out through the inspection hole.

This will be gross.
posted by flabdablet at 11:48 PM on February 19, 2020 [6 favorites]

This could also indicate that the plumbing vent system isn't venting. If cleaning out the trap(s) don't resolve this, look for an under-sink vent system and/or check the pipe coming out your roof for obstruction.
posted by achrise at 6:22 AM on February 20, 2020

If the sink is generally slow to drain and there doesn't seem to be a blockage in the under-sink U-bend and the ventilation seems to be in good shape, there's probably a fatberg a bit further down the drain that will need snaking to shift it. A small and flexible hand snake will probably do a much better job on a kitchen sink drain than a great thick power snake; these often have trouble negotiating the tight U-bend that might be encountered if there's a gully trap or grease trap somewhere down the line.

And gross though the contents of the undersink U-bend undoubtedly are, they will be as nothing compared to the stench of what will be stuck to the snake after dealing with an in-drain fatberg, especially one fed regularly on a diet of minced everything.
posted by flabdablet at 7:15 AM on February 20, 2020 [1 favorite]

To add to flabdablet's hot water clearing: I have had very good success keeping my drains clear by occasionally dumping boiling hot water down the drain. We've had a tough time with my old house's drain. The morons who laid out the plumbing in my house have a no-slope 90° bend to the drain in my wall. This represents 3 feet of gravity-unassisted clogpipe. Since there's a garbage disposal putting all manner of food particles in the drain, it's been a challenge to keep it clear.

I never run any plant scraps down the garbage disposal. They all go to compost. The only things that I tend to grind up are inedible meat scraps, heavy in protein. I never dump fat or grease down the disposal.

Even with my precautions, every couple of months or so I'll notice the drain starting to fight me. It is then, before the clog happens, that I must drag out my trusty huge stockpot, boil as much water as I can fit into it, and dump it down the drain. I turn on the garbage disposal as well, to generate a bit of pressure in the drain to force the boiling hot water to clear the clog.

This procedure works extremely well to clear my drain, with a caveat. The pressure generated by the garbage disposal's centrifugal pump has blown out my drain's compression fittings, creating a huge mess. The boiling hot water I use softens the pvc drain pipes just enough to allow this to happen. I've got a little prop holding my J trap so this can't happen anymore.

I wish you luck at keeping that drain clear.
posted by sydnius at 7:35 AM on February 20, 2020 [1 favorite]

The first thing you can do is put a lot of hot water down the sink, and if you're in a house or structure with individual drains that meet up at a single point of exit it can help (in the case of a fatberg between house and street) to do it from multiple vectors, so boil a big stock pot of water on the stove while you run the sink and shower hot for 5-10 minutes, then dump the boiling water down (I think you're not really supposed to do that down the disposal side, so use the off side). I always add a healthy squirt of Dawn to the boiling water, probably out of superstition more than expectation, but there are also enzyme products that claim to help remove pipe residue. Don't use caustic chemicals because if this doesn't work, the next steps are going to require contact with pipe contents.

Disposals are a simple machine, they don't really do "wrong", but they are dependent on an expected pattern of airflow in the pipes to do what they do. When you have a partial blockage - and it might be immediately underneath the disposal unit, a few inches down in the trap, or a dozen or two feet down the line toward the sewer - and the full water level in the pipes creeps back up toward the drains, it's a little bit like pointing a hairdryer directly into your coffee cup when you run the disposal. The nearest freely-venting opening is the off-side of the sink, so that's where the ejection point is.

If you're in a freestanding or semi-detached house with the kitchen on the first floor, you likely have an external drain cleanout (mine have always been white, but otherwise that shape) on the wall outside the sink. There are also internal cleanouts that may or may not have that same cap (they may be built into the plumbing - you may be able to google/youtube your way through figuring out what you have and how to get at it). Those let you access the household drainage system directly without dealing with the actual sink plumbing assembly. Youtube will explain how to snake or flush via that outlet. This is where you want to NOT have used lye drain openers, because when you first start flushing and/or snaking there's going to be some...backsplash. Right into your face and/or all over the ground outside your house. Where you will spend days trying to keep your dog from licking the ground because they are not bright.
posted by Lyn Never at 7:48 AM on February 20, 2020 [1 favorite]

I have an older house and so even though I have a top-of-the-line disposal, I never use it to grind up anything on purpose. I run it periodically with hot water to clean out any bits, but lots of homes have plumbing that is only going to be negatively impacted by introducing so much debris into pipes on purpose. Slowly but surely, kitchen waste will cling to the sides of pipes, narrowing them and creating eventual problems. I send food scraps and such to the compost bin. Like "flushable" wipes, disposals mostly just serve to keep plumbers in business. I'd clear this clog with boiling water and pressure and then shift my food disposing to a non-plumbing route.
posted by quince at 1:15 PM on February 20, 2020 [1 favorite]