Dishwasher is filling up with nasty, septic water

[bfollowell]

My son's dishwasher was a disgusting mess. Nasty, septic water kept leaking back into the basin from, I'm assuming, the drain line, which connects to the side of their garbage disposal. The drain tube snakes up and down the side of the dishwasher, forming a large P-trap. How this much water is migrating back into the washer is beyond me. Their old dishwasher was in poor shape to begin with, so we had it replaced as a gift. Now the same thing is happening with their new dishwasher. I'd assumed there was some sort of drain valve that opened and closed as necessary, that wasn't working correctly on their old dishwasher, allowing this water to get back into the basin. Now that it's happening on their new one as well, it makes me think that the drain is just open all the time. Otherwise, I don't know how this water would get back into the basin. I've never had a dishwasher that didn't have a dedicated drain. Should there be some sort of check-valve where the dishwasher drain connects to the side of the garbage disposal?

Have any of you experienced this before? Any ideas?

[abaesemann]

This is the proper hook up under sink, the drain hose goes hi before going to dw or disposer. maybe you have a backed up sewer pipe that needs to have a plumber rooter out.

[abaesemann]

[16345Ed]

Or a missing or failed check valve... 

does it drain? Can you hear or see water going into sink drain?

[TurtleRock]

Also if your sink drains slowly it may siphoned into the dishwasher drain. 

[bfollowell]

Their dishwasher/sink doesn't have an air gap, and the existing drain line was just ran straight through the bottom of the cabinet and up to the disposal, not up to the underneath of the countertop like you guys showed. I'll definitely have them run that drain line up and, the next time we visit, I may drill a hole in their sink and install an air gap, just to be safe.

Thanks.

 

[Econo Appliance]

1 hour ago, bfollowell said:

Their dishwasher/sink doesn't have an air gap, and the existing drain line was just ran straight through the bottom of the cabinet and up to the disposal, not up to the underneath of the countertop like you guys showed. I'll definitely have them run that drain line up and, the next time we visit, I may drill a hole in their sink and install an air gap, just to be safe.

Thanks.

 

That's your problem right there.  Just run a "high loop" in the drain hose, problem will be solved.