Kitchen drain backup with dishwasher

[egor]

Kitchen sink backs up into other sink when dishwasher or disposer run and drains slowly. Trouble started when we added dishwasher and disposer. I have 10 inches of drop from sink to trap is this enought? Replace inline vent about drain trap, checked 1.5 inch line it,s clean and has 1/4 inch drop to 4 inch line. Have 20 feet of 1.5 inch line to 4 inch line. Is this line too long? Does 1.5 inch line have enough volume to handle dishwasher and disposer? Should I go to 2 inch line to handle the volume?

Thanks
egor

[krow]

My money is on your "inline vent". Technically they should not be used in most juresdictions. The vent should really connect to a natural vent that goes up to and through the roof. You can test that vent/drain by simply removing the avv and try using your dishwaser and or disposer. If it runs good, then that is the problem.

[egor]

Added hight to vent and check complete system. All system go!
Thanks
egor: