Sewer smell from washer area

[csp]

On a 95 dynasty every once in a while we get a sewer smell from the cabinet where the washer is. It never seems to do it the same time (after shower washing clothes etc.). It may do it once every week or twice in a day. I checked the plumbing behind the washer and checked the vent valve next to the toilet and they seemed to be fine.
Any advice would be helpful.
Thank you Chris

[Dogpatch]

Add some water to the down pipe. The P-trap is probably empty allowing sewer gas to exit the tank.

[njs42]

P-trap dry-or in our case the outlet hose for our washer dryer was pushed so far down the drain pipe that it went past the P-trap. Pulled it out and cut it off about five inces below the top of the drain pipe.

[csp]

Thank you for the help. I figured out the problem. The vent pipe going through the roof was even with the roof vent. When the weight of the water was in the pipe it sagged down just enough to let the sewer gasses into the coach. I fixed this by cutting the vent pipe in the closet and adding a rubber boot. This allowed me to raise the pipe up enough through the roof vent that the slight sag with the weight would not let in the sewer gas. I also put a bead of silicone around the pipe to completely seal the gases out. So far it has been sew gas free.
Hope this helps out anyone with this type of problem.
Chris