Whenever my washing machine drains, it blows sewer gas out of my kitchen sink. The house is single story with a single sewage pipe running from the rear of the house to the middle where it exits. The washing machine is the last thing on the line (rear of house)and has a p-trap. The kitchen sink is the next after the washer. Sink has a studor(?) vent on it as well as a P-trap.

Any idea why this is happening? And more importantly, how can I fix it?