Apparently the OP is one, that when given good information, chooses to
ignore it. I still wonder why they ask in the first place. I hope I
never have a neighbor like that, trying to bring the property values
of the neighborhood down, every time they pick up a tool.
Where is the "good" information?
All this talk about code and traps and air vents is nice, but it doesn't
speak to my primary question.
I want to know if dishwashers depend on having the discharge line rise
above the level of their drain-pump outlet before the connection point
to a drain pipe. This bit of plumbing may not be seen or noticed by
most people since it can happen inside the machine's chasis or
I happen to be routing the discharge line directly through the floor
under the machine, and the drain-pump outlet is just inches above the
I know I can route the discharge line up inside the enclosure for some
distance (2 feet at least) before looping it back down through the hole
in the floor. But I'd like to know if dishwashers depend on such an
arrangement or not.
So you're saying that I shouldn't expect an answer here from someone who
might be a plumber - or who is otherwise well-informed or knowledgeable?
Why does this newsgroup exist, if the pat-answer to all questions
(according to you) is to ask a (plumber, electrician, pipe fitter,
roofer, brick layer, engineer, chemist, contractor, lawyer, doctor, ...)
Qualified electricians, plumbers, etc., keep up on these things
because it is necessary for their job. I might remember what was up to
code when I installed an appliance back in 1982, but many code changes
may have come about since. I was not being a smart ass for suggesting
an expert in the field of plumbing but perhaps to help you avoid an
error which could cause financial or even health problems in the
You have to admit, this thread has been running for a long time, and
no one has answered your exact question. IIRC people have even
disagreed with some of the things that were said.
I don't remember anyone here being a licensed plumber.
I think about 20, 25 years ago, someone wanted to discuss home
repairs. Either that or someone just put it on the list, even though
he personally wasn't interested.
But it's not the answer or an answer given to all questions. It
wasn't even the only answer given in this thread.
You have been given the following "good" information several times:
2. Get professional help.
Your choice is probably going to be "3. None of the above, I'm fully
capable of screwing things up all by myself".
In the drawing but the text says the minimum is 30 inches. I think in
practice the easy place to put the air gap is at the rear of the sink.
Why not? I have one. It doesn't get in the way. The air gap is the
whole point of it. That's what stops the siphoning**. BTW, I once
had a little chicken bone, the one next to the drumstick, in the
air-vent and the dishwasher would not drain. It took a while to find
the problem, and I'm still not sure how this little bone kept it from
**although I'll admit, I havent' figured out when there would be
siphoning, or even in which direction. Stuff that would go into the
dishwasher woudn't be siphoned in, I think. Maybe it is there to stop
the water in the bottom of the dishwasher from being siphoned out????
I'll have to look at that.
Yes, the toilet would overflow first if the backup was in the 4" line.
| I can't believe that something as simple as whether or not a dishwasher
| drain hose must always form a loop (inverted trap) wouldn't be more well
| known if it was common knowledge.
One problem is that code requirements have changed over the years and
dishwasher (cost reduction) design has taken advantage of this. My
house's original dishwasher (~1959) was hard plumbed directly to a trap
in the basement. It had no high loop, no air gap, and no standpipe.
It did have a positive drain valve solenoid that closed the drain when
it was not trying to pump out water. It was also wider than current
dishwashers. As far as I know, that installation was to code at the time.
The first replacement dishwasher (in the 80's I think) was a KitchenAid
and while it did not have a drain valve it did use a separate pump for
removing water. It was happy with a high loop but still hard plumbed to
the trap in the basement. I _think_ the installation manual showed the
hard-piped trap as a valid (though not necessarily legal) configuration.
The next replacement (I don't remember the brand) in the 90's (notice
that life span is decreasing :) did not have a separate pump for removing
water. Instead it manipulated the circulating pump in such a way as to
cause a little plastic flap in a chamber to divert water out. This appeared
to depend critically on the back-pressure at the drain and I was unable to
make it work reliably with the hard-piped trap, regardless of high loops.
I was able to find a different brand that still worked with the hard-piped
trap, but I decided that that configuration's days were numbered so I
reworked the kitchen sink setup with a garbage disposal. The latest
replacement dishwasher has a high loop and empties into the dishwasher
port of that garbage disposal per the current preferred configuration.
IMHO, in general, a high loop saves you only if the drain hose opens
to air before it gets back as low as the highest water level in the
machine. This is the case with the garbage disposal port but not with
a hard-plumbed trap below the floor and not even with a standpipe below
| I'm not sure what that do-hickey is in the last diagram - identified as
| an "air gap" that seems to protrude above the counter top. That can't
| be a desirable thing to have poking through your counter-top.
As the name implies, it is a true air gap that both prevents siphon and
diverts any reverse sewage flow onto your counter (which is arguably
better than hiding it in the dishwasher). The aperture on the dishwasher
side is smaller than that on the sewer side. This is currently the
ultimate in safety and (I believe) required by code in some places.
Something I'm not clear on is whether you can use an air gap and then
hard-plumb the outlet to a trap under the floor. Somehow I think that
even with the air gap you are supposed to enter a disposal or open sink
As long as you are going at a continuous downward angle below the pump
it will siphon out just fine. It's when they drain into the sink drain
above the pump level that they need a loop above the drain level to get
siphon action to completely drain the dishwasher.
That's the problem. I'm wondering if the water is siphoning out when it
I can understand that the recommendation is that the drain hose make a
loop going up to above the level where the sink water-line might be - to
prevent the sink water from draining into the washer.
But if you don't have to worry about the drain from a sink (because
there isin't one nearby) then do you still have to worry about water
draining out of the washer when you don't have a rising loop in the
Not sure I would make a direct connection to the drain in the basement. I
would probably add a stand pipe with trap and air vent much like I was
plumbing for a clothes washer. I would raise the drain to the dishwasher to
just below the countertop before heading to the basement simply because
every dishwasher install instructions that I've seen says to do it. Most
instructions allow increasing the hose length if needed.
(I don't have a countertop - this is a portable dishwasher that I've
parked in the corner of the kitchen).
Do they recommend it to prevent the sink from draining into the washer,
or because the washer needs the drain line to go up first before it's
connected to a drain pipe because it can't stop water from siphoning out
Your lights go out because a 15 amp fuse blows. Following your logic,
you put in a 30 amp one because it's convenient. The lights are back
on. Problem solved.
There is a reason why code requires a trap and vent on drains.
Several people here have tried to explain to you why what you're doing
can and likely will result in sewer gas entering the dishwasher and
living space. But that doesn't concern you.
Going up first doesn't stop a siphon from working. I can place one
bucket of water 15 feet higher than another. Take a hose, fill it
with water, put it in the high bucket and let the hose rise another 2
feet above the bucket. Put the other end in the lower bucket. The
water will still siphon.
The high loop is there so that if the sink drain backs up, it will
rise into the sink first and will only get to the dishwasher if it
rises clear to the top of the high loop, ie as high as the bottom of
the counter top. For it to rise that high is quite unlikely and
someone will likely notice the backup, as opposed to it going unoticed
and just contaminating the dishwasher.
But, why all the concern? You obviously don't care about doing
plumbing to code when there is an obvious and very good reason for the
code, ie a trap and vent to prevent sewer gas from coming into the
house. The dishwasher seems to be working, so just do it your way.
Replace the word "siphoning" with "draining" above.
I don't have a sink drain. The dish washer is not competing with a sink
in this case. The washer is located in a corner of the kitchen away
from the kitchen counter and sink. The dish washer is not sharing a
common 2" drain pipe with an adjacent sink.
I've explained many times - I've arranged it so that the dish washer
discharge line is fed directly DOWN from the drain pump outlet through
the floor to a dedicated 2" ABS line that runs at a slight down-angle
for 10 feet to a connection on one of my primary 4" vertical sewer pipes
that runs into my concrete basement floor.
If something backs up on that 4" line, then I've got more of a problem
that could ever be solved by having a proper dedicated trap and vent for
Because my washer does not seem to be operating properly - it seems to
need to have water added at times during the various cleaning cycles as
if water is leaving it for some reason.
I'm wondering if the water is draining through the drain pump because
there is no "up-loop" in the discharge line.
You can hook it up with or with out the loop. If it works without the
loop good deal, if the water drains out as it fills then make a loop.
I'd do the loop anyway, bugs have a habit of crawling inside and up
anything they can and you might find a bug or two in your dishwasher
someday, if there is an air gap to the floor drain in the basement there
shouldn't be much chance of sewage contamination. If you and your family
are healthy a year from now, no problem! Me I'd want to make sure there
isn't sewer gas getting back to the dishwasher. A trap as close as
possible is the best way I know of to do that and the machine gets
plenty of hot water (that is really good at killing or reducing germs)
and dissolving fats. FWIW I always throw in some water in before
running my dishwasher, lubricates the seals before the water gets around
to flowing in, starting the dishwasher dry is a good way to shorten
it's life. I also turn on the hot water at the faucet to get the hot
water at least that far, then shut off the faucet so the dishwasher can
start with hot water coming in.
And finally the purpose of requiring licensing of plumbers is to
protect the public water supply. It is possible that an incorrectly
installed dishwasher (or anything) could be contaminated with sewage or
chemicals, then an improperly connected water supply via the plumbing
can back feed to the public water system causing contamination of the
public water supply system. It usually takes a chain of events for this
to happen but it does, nail, shoe, horse, soldier, battle kind of
thing. google "water supply cross contamination" if you are interested.
There are lots of examples of this happening. You just might be
drinking your neighbor's sewage or the chemicals he sprayed on his lawn.
Now go forth and get the dishes washed. What are wives good for
anymore? Aren't they supposed to wash the dishes?
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