Do dishwashers need drain hose to rise above level of drain pump?

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FatterDumber& Happier Moe wrote:

Ok, so I guess nobody's gonna answer that.

So how exactly can contaminated water overcome the somewhat high water pressure of the municipal water system and backfeed into my water pipes and spread to adjacent houses?
Wouldn't I need
a) a tank of at least 5-10 gallon capacity, filled with dirty water b) a compressor or pump to take that water and inject it at high pressure back into my main water supply line c) the intent to put those items together and make it happen
How else could contaminated water flow back into the water supply system?

Where did I say that I was on well water? I'm not.
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Sum Guy wrote:

Where did I say you waz?
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FatterDumber& Happier Moe wrote:

You said:

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
How could I be "drinking the chemicals he sprayed on his lawn" if both he and myself are served by a municipal water source? Even taking into account that I don't have a trap on my dish washer drain line?
And you didn't respond to the other comment I made about your last post:

So how exactly can contaminated water overcome the somewhat high water pressure of the municipal water system and backfeed into my water pipes and spread to adjacent houses?
Wouldn't I need
a) a tank of at least 5-10 gallon capacity, filled with dirty water b) a compressor or pump to take that water and inject it at high pressure back into my main water supply line c) the intent to put those items together and make it happen
How else could contaminated water flow back into the water supply system?
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Well, if Saturn is behind the moon and the temperature is below 50 degrees and your roses bloomed and . . . . . .
Backflow preventers are required by code for lawn sprinkler systems, boilers that use chemicals, pretty much an process that is connected to a municipal water supply. The fear is that if the town water pressure drops you can even get a vacuum that willd raw contaminants into the system.
In the case of a dishwasher, the drain would first have to back up into the wash chamber, (getting past the drain valve) and then past the solenoid operated valve on the supply line, then sucked into the supply line as there is no pressure to force it. I'd say it is a rather unlikely scenario.
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Ed Pawlowski wrote:

Does that include installing one at your dish washer or clothes washer?
The truth is that even if my (somewhat large city, not town) water supply pressure fails (which has never happened in my living memory) I garantee you that when it comes back that they'll tell people to run their taps for several hours anyways. They'll treat the system as if it *is* contaminated.

Agreed.
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Some towns are trying to do just that. Every home would have one at the meter. Seems like a rather expensive cure for a non-problem.
I've never heard of anything like it ever happening, but our society wants to protect us from every possible scenario, not matter how slime the odds of it happening.
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Water systems do fail and loose pressure. When a city makes an announcement do you suppose every resident hears it?
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Pat wrote:

When they've lost water pressure, and they're glued to the (TV, radio, newspaper, etc), then sure they're going to catch such an announcement. It will be big news. Some sort of catastrophe would have caused it.
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If there was a fire and the fire truck hooked up to a hydrant close enough it could cause a negative pressure and thus suck water out of your pipes

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don &/or Lucille top-poasted:

Did you have to full-quote me, just to add that ridiculous scenario?
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Ridiculous?
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wrote:

Care to elaborate? ==
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May sometimes and may not sometimes. What happens when you turn on a vent fan sucking air out of the house?
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In typed:

Here's a novel approach: RTFM! It even explains the siphoning action and why it happens in 99% of the cases.
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No shit Sherlock, There was discussion about why the high loop was called for in dishwasher installations. That was the point. It's perfectly clear that you not only don't have a sink, but in fact are connecting the dishwasher drain straight downhill into a sewer pipe without a trap. I think just about everyone here will tell you:
A - That's a clear code violation
B - It's one code where the reason for it is clear and it makes perfect sense.

Sigh... Once again, traps in sewer systems are not there to prevent your sewer from backing up. They are there to prevent SEWER GASES FROM ENTERING YOUR HOUSE every day. If traps aren't needed, why the hell does every sink, washer, toilet, etc have one? You're concerned that water may be running out of the dishwasher, but not that sewer gas can be coming back in? Sounds great. Cleaned dishes sitting in a closed dishwasher, exposed to sewer gas.

If it's behaving that way, then it could very well be happening. Do you think every dishwasher uses exactly the same pump out design? No one here is gonna know how your dishwasher, which you don't even indicate the make or model is going to behave when you use it in a way MOST people never would. As others have suggested, you could go to the manfacturer's website and see if you can find an owners manual. But even that will probably not answer the question. They will show how it should be installed, but likely won't tell you what happens if you do it another way.
But instead of speculating, why don't you just put a high loop in it temporarily and see if it then works correctly? And regardless, get a trap and do it right.
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snipped-for-privacy@optonline.net wrote:

I've never argued against the fact that traps are needed and perform an important function.
Yes, for fixtures like sinks and toilets that would otherwise have a direct, open-air path to the sewer, the traps prevent an open-air direct path.
But dishwashers and even clothes washers don't have such an open-air path to a sewer pipe. They have pumps and maybe even solenoid valve blocking that path.

When the dishwasher is running and circulating water, then obviously there can't be a direct open-air path from the inside of the washer to the sewer pipe, otherwise the water would immediately drain out.

Kenmore portable, purchased fall 1996. I found the operating manual and installation instructions. The model numbers on the manual don't match the number on the decal on the washer. There is no mention of hose-routing concerns in either manual. Probably because it's physically impossible to route the drain line at a continuous down-angle from the pump given a "normal" installation.

Correct.
That I will have to do. I just thought that I wouldn't have been the only one here who would have run a dishwasher discharge line directly down through the floor below the washer.

By adding an "up-loop", I am effectively forming a trap inside the washer that will always contain some water. Or do you dispute that?
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No, you just say you're gonna do it without a trap.

You have enough knowledge of the design of that pump to know that it can't let sewer gas through? Does the plumbing code say it's OK to rely on what you're doing instead of a trap?

Yes I dispute that. What you will have isn't a trap. It's an upside down trap. When the dishwasher is done pumping, water on the sewer side will run into the sewer. It will likely siphon the rest of the water from the dishwasher side with it. Or the water left in that side could run back into the bottom of the dishwasher basin. That leaves the hose empty.
I can just imagine what other improvisations you have made that are illegal.
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snipped-for-privacy@optonline.net wrote:

And the pump will not likely be able to push ALL the water over the top of the loop, so when it turns off, the water that was trying to make it up the rising part of the loop will fall back into the pump and the drain reservior, as happens with conventional under-counter installations. That water will form a block, preventing a direct air path between the inside of the washer and the sewer line.
I say that the pump will not likely be able to push all the water up the loop because ventually the pump will suck air and it won't be able to push the air and remaining water up the loop and over the top (the pumps are probably not air-tight).
Take a hose and try to blow some water up over a short loop and out. You won't be able to, unless you've got a source of compressed air behind you.

Siphon action won't pull all the water up and over an up-loop. Some will fall back. Enough to form a trap.
In fact, according to your theory, even conventional traps should siphon and empty out if that was the case. But they don't.

No, the lowest part of the hose wouldn't be empty if the water ran back downhill into it.

You should see my furnace...
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Just tell us one thing smart guy. What does the plumbing code say about what you are doing? What would any home inspector say when he spotted a dishwasher or washing machine that was tied directly into the sewer with no trap?
And if you're so smart, and know so much about what can or can't pass through any dishwasher pumpout system, why are you here asking about high loops?
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snipped-for-privacy@optonline.net wrote:

Building codes are based on engineering principles.
We are discussing the fluid engineering principles of dishwasher drainage.
What we theorize about what is needed for the correct and safe operation of a dishwasher drain system should be (but may not be) described in the local building code.
As far as I can tell, this is a copy of the building code for my jurisdiction:
http://www.hastingshighlands.ca/upload/newdocuments/Building%20Code%202007.pdf
It does not specify if a trap or air gap or air break is needed for a domestic dishwasher.
This thread:
http://www.inspectionnews.net/home_inspection/plumbing-system-home-inspection-commercial-inspection / 20168-dishwasher-directly-into-trap-crawlspace.html
(re-assemble the long line as necessary)
has a post that says this:
------------- Here is what the NC plumbing code says -
802.1.6 Domestic dishwashing machines.
Domestic dishwashing machines shall discharge indirectly through an air gap or air break into a standpipe or waste receptor in accordance with Section 802.2, --------------
An air gap (or air break) is presumably formed by an up-loop in the drain line. I believe this is an acknowledgement that such an arrangement would always lead to some water sitting in the dishwasher basin and pump, effectively forming it's own trap.

Again, any appliance that has it's own pump may require that it's discharge line rise to some level relative to the top of the device before being connected to a drain pipe or drain stack. I'm not aware that washing machines need their own trap (if installed remote from a sink) and I've never installed the pumbing for a washing machine.
And besides, as a home-owner, I don't have to know or follow the code for things that don't need a permit.

It's not a question of being smart. If you understand that the plumbing code is trying to enforce a certain engineering principle (that there should be no direct air connection between the sewer air and household air) then we can theorize how such a connection does (or doesn't) happen when considering a given dishwasher drain configuration.
Since I'm NOT smelling sewer gas in my kitchen or in my dishwasher, I think we can move off this tangent and get back to my original question, which is:
Do dishwashers depend on their discharge line running up from the drain pump and forming an up-loop before falling down to make a connection to a drain line? Do they depend on this arrangement to prevent fill water from draining unintentionally from the machine?
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