Yes, frodo here above, and live_wire_oak in the other thread (linked to above) got it right. -- 99.9% right. I'll add a bit of context, based on my knowledge of DWV plumbing. I am happy to share and to read feedback, and I don't mind plumbers telling me more.. An indirect connection (before _Any_ P trap, not just the sink's P trap) lets air in or out, preventing the draining water from sucking open either the P trap or the DW's base (its "sump") which is supposed to have some standing water left in it. ((Note that doing the opposite would have the same effect as two P traps in series which is disallowed)). An indirect connection is a set up that lets the drain gurgle: it mixes with room air. It can look like a standpipe (that looks like your clothes washing machine's standpipe) or it can look like some other set up that looks_different but does the_same thing. This is why your DW makes gurgling noises in the kitchen drain pipe when it drains: it is pumping water into the drain prior to the P trap, so you hear it. It is not allowed to connect the DW drain to your plumbing behind a P trap, it must be in front of a P trap. You Are allowed to send the DW drain hose from an Air Gap directly to the kitchen drain without going through the garbage disposal first. The option to route through a disposer is one optional route. It is one option out of a very limited number of options. A "High Loop" brings the DW drain hose to the house plumbing before the sink P trap also, and in the sink drain is where the gurgling / air-mixing takes place, and that is where you will hear it. A dishwasher _Wye or _Tee is the connection part usually used but any Wye will do. A third option is if you install a separate stand pipe like a laundry standpipe: then that means a separate P trap which then presents other (minor) challenges, since it has to be connected with the right venting behind the P trap; this is venting for sewer gases (not room air venting) which is the usual meaning of venting when plumbers talk to plumbers. When a P trap is under the floor, the drop may be too far and the P trap may self-siphon because the fast moving (falling) water will all slide out. That is inertia because of the fall. However, it is not disallowed, it just calls for a professional plumber or a highly knowledgeable homeowner. (So yes, sometimes a P trap in a basement for a fixture on the first floor can be good; e.g. if it is right under the floor, up against the basement ceiling, and with the right venting too!) As live_wire_oak said in the other thread, this is all part of the plumbing code for health and safety reasons. Sewer gases cannot be allowed to enter a house, so P traps which could siphon themselves out are disallowed, and this is all an exercise in 3-D geometry including the drain diameter. Plumbers spend Years learning this and writing exams, so don't let a plumbing apprentice design your DWV plumbing, and double-check everything even if you think your plumber has all the answers, as they do make mistakes too. I have seen this more than once. The 3D thinking involved is complex, even for a new building where everything is built as a system all at once, but even more-so for a reno or remodel where the "system" is not all visible and sometimes not even fully understood. Above I mentioned that you would hear the DW drain gurgling. If one built a standpipe that got its air from up high in the dropped ceiling, the gurgling noise would be minimized. It would be a tall pipe with a Wye in it to receive the DW hose. HTH -david

"... is it acceptable to create a high loop for the dishwasher drain line by passing it through a high hole in the cabinet, or is it necessary to use a low hole in the cabinet and then use a strap to make the high loop?" AFAIK in areas where the high loop is permissible you start low then go high under the counter top and then down... hence the name high loop. Starting high then going down would not achieve the same thing as a high loop. I defer to those licensed plumbers on the forum for the final word. Air gap may be required in some localities or not and high loop may be permissible in some localities or not. It isn't what you want to do or what is easier or more convenient or what someone tells you is OK. If you want to do it right (according to local code) then check with a local plumbing inspector or look it up in the governing plumbing code yourself.

zl700l, I don't believe there would be anything in a dishwasher that would be sufficient to act as an effective p-trap and I do believe you are basically bathing the dishes in your dishwasher in sewer gas, not to mention airbourne bacteria. The explosion risk of the methane entering the dishwasher is not to be ignored either, I am sure there is plenty of potential ignition sources in there to be of concern, moreover, people die in homes infiltrated by sewer gas. The risk is not to be scoffed at. Moreover, it's just common sense- the practice is dangerous and illegal, makes your house unmarketable and subject to being condemned or remediation orders, and just a bad idea. We're talking about a little gurgling water, not freeway noises. I like hearing the dishwasher when it drains because a) I know it's working and how far along it is, and b) having it drain into the p-trap means that it's charging it (keeping it full, avoiding gas infiltrations) and the dishwasher detergent going through the trap keeps it clean and smelling decent. As the the 'banjo' vs 'my house is bigger than yours' contest, I don't believe in being rude as it were but I believe it's not a question of how much money someone has, but how much common sense /stubbornness they have.

I live on the East Coast and I see them all the time...I guess this is why I am so adamant about avoiding the countertop air gap. No GW-ers probably don't notice, but I think we are all TKO and totally observant. Thank you everyone for your posts. Very helpful. After reading my kitchen aid brochure for installation, I see that there are two options 1. with air gap 2. without air gap Theres no mention of a situation/why you could install without an air gap. Davidro- thanks for clarifying that it is not model specific and more personal preference. I'll speak with the plumber and determine what our true options are. I have no idea what our code stipulates. If the plumber doesn't know, then I guess we have bigger issues than an air gap :)