Sewer stink from dishwasher

[HeavyStella]

I am an experience DIY plumber and this one has me stumped. Drain for dishwasher is tied in before the kitchen sinks P-trap (upstream) and when we open the dishwasher sewer stink comes out. All experts would say "you have the dishwasher drain after the trap and that's why you're getting the stink". This isn't the case! Also the trap isn't being siphoned dry by waterflow because there is no stink from the sink's drain! I clean all the mechanical filters and stuff in the dishwasher a couple times a year and we're good for a week or two then the stink is back. I can't believe a bit of residue in the dishwasher's pump could be creating this vile stink but maybe that's the first thing to hit. Anybody else heard of a dishwasher pump that doesn't evacuate the dishwasher 100% and leaves some gunge to fester? Thanks in advance
for your viewpoints!

 

[LiQuId]

this occurs often and at first i was going to say the thing about the p trap tie in but if thats not the case then it could be stagnent material in the dishwashers outlet line.. is it a corrogated line ? often these will capture some of the debris that should be washed away, try running the dishwasher without anything in it to purge the line and if this works then, my friend you may have to get on the household to pre rinse the dishes a little better before putting them into the dishwasher. often times dw's will have some amount of stagnent water left behind but it does not usually cause a "sewer" smell.