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

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Sum Guy wrote:

http://www.inspectionnews.net/home_inspection/plumbing-system-home-inspection-commercial-inspection /
I vote yes.
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== If you don't set up the dishwasher drain in a similar manner as washing machines require, then we can assume that you don't care to do the installation to code specifications and are potentially endangering your health and that of others in your household. Stubbornness on your part may result in unexpected circumstances where the local authority could hold you liable for damages and extract a monetary penalty. ==
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Roy wrote:

Tbat is a *non-answer*.
I want to know if the correct mechanical (hydraulic) operation of a dishwasher requires a certain way to plumb the discharge line.
You keep wanting to talk about code. Fuck the code.
The code doesn't speak to the plumbing requirements of the device in question.
I posted a link to the code of my jurisdiction. To my reading, it doesn't talk about how to plumb the discharge line of a dishwasher.
So stop pedantically talking about code and put your engineering hat on and consider the device in question and it's engineering requirements. If you're incapable or unwilling to do that, then just say so, and this conversation is over.
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== Okay, when I bought this old house there was no provision to drain an automatic washing machine properly. I drilled a hole through the floor for a standpipe following the directions from the machine manual for its height. The black poly standpipe went through the floor and into a trap which was attached to about a six foot horizontal pipe with a bit of a drop which attached to the main vertical sewer main using the proper fittings. All of this was held up by straps which were attached to floor joists in a number of spots. Of course the vertical stand pipe was attached to a wall as well with the proper strapping to prevent it from wobbling around. All connections were roughened and the proper adhesive used to ensure a tight leak-proof seal.
Since you are using a "portable" dishwasher much like the one I have here but no longer use...the drain is probably incorporated with the filling connection, right? This small drain hose could be disassembled and routed to a similar standpipe with the same setup as I described for my washer setup.
When your dishwasher drained, it would pump the water down the pipe which would be as high as the top of your dishwasher (or close to that height). You would have the protection of the trap in the basement preventing sewer gas from rising to the dishwasher level and an air gap in the top of the standpipe as well which would prevent siphoning. Draining from the bottom as you proposed could easily cause problems in my estimation.
You would probably need an extension to the present drain hose with a simple adaptor (any hardware or plumbing shop could supply), as you wouldn't want it to fall out but it should go into the standpipe for three or four inches anyway.
I still say, take a rough drawing to a plumbing shop and get their advice. Most plumbers will give SOME tips without charging for it or getting annoyed. Some will even come out and give you a free estimate for the renovation project should you find it too daunting.
Happy adapting...over and out.
===
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After adding an extra 4-foot section of drain hose to form an inverted U loop up inside the back of the dishwasher, the washer now operates much better - more or less correctly when it comes to maintaining the fill or wash-water during wash cycles.
Something else that was happening (before the loop was added) was that the motor would make a loud squeeling noise at the end of every drain cycle - probably caused by a complete evacuation of water from the washer basin. This noise doesn't happen any more, presumably because the discharge pump can't push ALL the water up and over the loop during the drain cycle.
So I would conclude that dish washers needs the drain hose to rise to some level above the level of the discharge outlet in order to prevent fill or wash water from draining out of the basin during wash cycles because the discharge line is not really fully sealed off from the tub basin drain.
This arrangement of having the drain line rise to some level (1 foot? 2 feet?) relative to the bottom of the washer is normally accomplished by plumbing the line into a nearby sink drain line, which are normally set high up under the sink. Many people think this is necessary for the washer drain line to be connected before the sink's own trap, but it's clear that the washer's drain hose will form it's own trap either in or slightly below the drain-hose outlet.
But I've found that even that trap is not needed (from a sewer gas POV) because there isin't enough of an open path between the sewer line and the inside of the washer compartment to allow for sewer gas to enter the washer very easily.
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Thanks for clearing that up
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== I said it before and I will say it again...put a trap on the drain just below the floor level. cheap insurance and not much extra work. ==
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He clearly doesn't want to listen to that message or follow basic plumbing code. And I'd also point out that he still hasn't gotten the message that the drain line in a normal installation installation isn't supposed to go directly to the sink drain plumbing. It's supposed to have a high loop, taking the discharge hose up to the bottom of the countertop to prevent waste from flowing unoticed back into the dishwasher from a partially blocked drain.
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On Aug 12, 6:57am, snipped-for-privacy@optonline.net wrote:

== Yep, he is a stubborn one...I hope he likes dishes splattered with raw sewage. It can happen. ==
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Roy using bad form unncessarily, massively and lazily full-quoted:

I challenge you to explain how.
How sad it is that you think that a simple trap can prevent a sewage backup into an upstream fixture, or even that that's what a trap is for. Your knowledge of plumbing hydraulics and physics is pathetic.
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snipped-for-privacy@optonline.net unnecessarily full-quoted:

That actually wouldn't have solved the problem of water draining out of the washer when it wasn't supposed to. A rising loop inside the washer was needed to solve that problem.

And you are showing how ignorant you are of understanding basic hydraulic principles.
A dish washer isin't a sink or a toilet. Maybe you don't understand why those fixtures need a trap. And you certainly don't understand how a trap is formed by the washer's drain hose when it's arranged as a simple rising loop or inverted U.

And you continue to fail to realize that I do not have a situation where a nearby sink drain is competing with the dishwasher as far as draining is concerned.
If I don't want water in my sink to flow into my dishwasher when the sink is draining, then a high-loop for the dishwasher should prevent that. But when there IS NO SINK involved, then the high loop would also not be needed. Except that the washer needs the high loop for ANOTHER REASON - to prevent wash water from draining out the bottom of the tub during the wash cycle.
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Having a degree in engineering, I understand hydraulic principles quite well. Apparently you don't because you are the one that came here asking why your dishwasher installation that is in violation of plumbing code and practice doesn't work.

You came here asking how the pump out system in your dishwasher works, without even identifying what make or model it was. Only an imbecile would think every make from Bosch to Kitchenaid all share the same design and have had the same pump-out design over the last 20 years.
I understand that a high loop was never intended to serve as a trap. That's because the "trap" isn't one at all. It's UPSIDE DOWN. You do understand the concept of gravity, no? Water on the side connected to the waste system will empty. What happens on the dishwasher side is anyone's guess unless you fully understand the design of all dishwashers. You obvioulsy don't even understand the design of yours, because you came here asking about it. Now you want us to believe that the dishwasher side of the high loop will function as an upside down trap. No one here knows what multiple paths there may or may not be in the pump system of your dishwasher that might leave the dishwasher side of the high loop empty and allow a path for sewer gas to enter. Who says the hose stays full of water or where the water may wind up in the dishwasher once it shuts off? Yes, in some dishwashers the hose may stay full. Apparently relying on that warm fuzzy feeling to keep sewer gases out of your dishwasher and house is enough for you.

I and it seems just about everyone else here understands exactly what you are doing. You are broadly proposing that all dishwashers do not need a proper trap on the waste system based on pure speculation, without even knowing the internal plumbing of your own.

Again, you are clueless about how exactly the plumbing inside your dishwasher is laid out and whether in fact it can be relied upon to always form a seal against sewer gases. Why don't you call up you local plumbing inspector and ask him the simple question of whether or not a real trap is required when you install a dishwasher or clothes washer, etc. Everyone else here knows the answer. So stop saying "It ain't a sink or toilet." Because last time I checked a waste system trap is ALWAYS used on dishwashers and clothes washers. Are you just too cheap or too pig-headed to do it right?
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On Aug 13, 8:25am, snipped-for-privacy@optonline.net wrote:

== Oh...Oh...Sum Guy has gone silent...wonder if the sewer gas got to him. ==
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Roy full-quoted:

Cheap insurance - for what?
What am I insuring when I put in a trap for a dish washer?
Haven't I already said that there are no sewer gasses entering my dishwasher as-is?
Haven't I already said that the vent-stack going through my roof presents an ultra-low resistance path for sewer gasses compared to the pump mechanism of my dish washer?
Or are you too dense to comprehend the physics at work here?
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== Plug up your vent pipe with an accumulation of ice or snow or a bird's nest and see where your sewer gas will go. Do sewer gases only go in one direction? When the sewer gasses get to your drain pipe do they just rush by and not enter? There is nothing stopping them, right? Why do you not want to "build to code"? Don't you believe what plumbers have said about your "amateurish" plumbing job? I excelled in physics, did you even study it at all? ==
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No. In a normal installation the drain for the sink is above the water level in the dishwasher so the machine will not drain in this manner. The loop negates the need for an air gap. However in your case the loop would probably help prevent such drainage. Your installation dropping thru the floor into the basement may well create a strong siphon action preventing the loop from functioning as it should. An air gap may be required to break the siphon. A trap and vent is needed in the basement. A vent can be created using a one way air valve so the vent does not have to extended thru the roof.
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| 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.
As I said, I had a configuration like that for years. When I encountered a dishwasher that would not work correctly with it, a high loop was not enough by itself to solve the problem. I believe that if I had inserted an air admittance valve at the top of the high loop it would have worked, but it was easier to find a different brand that still supported the arrangement. That gave me a whole dishwasher life cycle to adjust the plumbing to the current expectation.
                Dan Lanciani                 ddl@danlan.*com
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