"Maybe the plumbing wasn't done professionally." With joints that appear to be between ABS (black) and PVC (white) it is very doubtful it was done by a plumber, and probably never inspected. There is no approved cement for joining ABS and PVC.

chillilover, do what zl700 said. Or connect it however it makes sense, to the drain pipe under the sink, but above the P trap. chillilover, you can disregard what joed said. I'll explain why. An indirect drain is by definition already in existence when you connect something (like a dishwasher) to the pipe under the sink, above the P trap. Search on this term : "Dishwasher Wye" or "Dishwasher Tee" and you'll see how millions of dishwashers are plumbed to sink drain pipes without even going thru the garbage disposer. There is air, open to the room, and this is the definition of an indirect drain. You hear gurglng coming up thru the sink strainer. Go see your washing machine standpipe and you'll see another indirect drain. It has air, open to the room, so that when drain water comes in, air can leave the volume occupied by the water coming in. You hear it gurgle when it drains. That is it. Nothing more. So, yes, it is correct to say, " should not be connected direct to the drain line..." but this correct information was not given to you in a way that made sense. The only way to "connect direct to the drain line..." is if you had a separate (dedicated) P trap for it --- which you don't have! Then, when joed said "An air gap of some sort would be required ..." he is again 100% correct, but it's information given in a way that creates confusion not clarity. An air gap already exists when an indirect drain exists. An air gap is a space that lets air come out when water comes in, so it is not a product to buy but a space to maintain. Again go look at your washing machine standpipe and you'll see that nobody taped shut the air gap (spacing) that lets all the gurgling noise (air) come out when the washing machine drains itself. So, yes it is correct to say "air gap required" but it is doesn't help understanding. EEspecially true, since you already got the answer you needed in the preceding post, so it appears more as a contradiction than as a confirmation. Duh. Since you asked about "check valve" it proves that joed's post appears to you more as a contradiction than as a confirmation that zl700 was right. Don't overthink this: just go connect it. hope this helps.

I've lived in and visited places where permits weren't required, or enforced, and the houses were about as hacked and unsafe as you'd expect. When you hear people say that government should butt out of everything, remind them of how important building codes are! If you live in a city, I strongly suspect that the people who did the work on your bathroom are giving you a snow job. The city needs money, and they're not going to forgo the income they get from issuing permits. :\ As for the problem, the above posts are right on, the drain system isn't vented properly or the vent is plugged. If vacuum pulls the water out of the sink trap, sewer gas will enter your home. That's a health and safety hazard. Get this fixed by a licensed, qualified plumber, pronto.

We most likely have a clog problem that we can't seem to resolve. These are the details: The drain has been slow in the tub in bathroom #1 (located on the east end of the basement of our ranch home) for a while, but it was always keeping up pretty close and finished draining within 30 seconds of the end of a shower. Earlier this week, the toilet in bathroom #1 plugged so my husband plunged it, and a bunch of stuff backed up into the tub (he thought it was from the toilet, but I questioned if it had actually come from the garbage disposal). After that, the tub was extremely slow draining, and then water started backing up in the floor drain of our furnace room (there is no sink in this room, but the water softener and air conditioner drain there, and it's in the middle of the home to the west of bathroom 1). You could run less than a pencil sized stream of water before the floor drain started overflowing. We tested each of the drains after that, and bathroom #2 (located in the middle of the basement to the west of the furnace room) has had no effect on it, nor has bathroom #3 (located on the main floor to the west of bathroom 2 ). The kitchen (located above bathroom 1 on the main floor), and the laundry room (located to the north of the kitchen) both cause the furnace room floor drain to overflow as does bathroom 4 (located just to the west of the laundry room). So far, we've tried Drano in the tub in bathroom 1, but that did nothing (we discovered the floor drain was backing up after we did that). We tried vinegar and baking soda in the kitchen, bathroom 1, and the floor drain and then slowly running water through, but that did nothing. We've tried dawn dish soap in all drains and then flushing them out (slowly in the drains that cause backups), but that did nothing. We tried a flat snake (loaned to us by a neighbor) through the floor drain, but we couldn't get it to maneuver the turns of the pipes. We tried forced air through the floor drain, but that just pushed back into bathroom 1 and started to cause a sewer gas smell. We tried leaving it completely alone for 24 hours, but that did nothing. We tried a 25 foot plumbing snake through the floor drain, but I'm fairly certain it kept going the wrong direction and kept heading east towards the bathroom rather than west towards the clog because it did nothing, and I can't imagine the clog is more than 25 feet to the west of the furnace room. We also tried the snake from bathroom 1, which likely only got us about five feet past the furnace room. We then got a 50 foot snake, and ran it through twice from bathroom #1, but nothing changed. I attempted to run it from the floor drain in the furnace room but I couldn't get it past one of the turns because the 50 foot one doesn't have an auger on it (the 25 foot one did which made it much easier to get through the turns). None of our other drains are affected after using the 50 foot one, so it's not like I just pushed the clog further. Is it possible we have two outlets to the house, and what are the chances the clog is 50 feet away from the originating spot? We checked each of the four vents through the roof, and they are all clear from a visual check as well. Is it possible the snake is taking the wrong route without coming out another pipe? We looked and listened for any signs of it coming through the wrong area, and didn't notice that with the 25 or 50 foot snake.