Help...Smelly water from kitchen sink

[LJS1211]

This is our 2nd trip in 4 weeks that we've had this issue and I can't figure out if it's our trailer or the park itself. We have a Vibe 250BHS and it has separate gray tanks for the kitchen and bathroom which is a definite plus. Issue is when we run water from the kitchen sink we get a very bad odor. We originally thought it might be the tank simce the DW let some broccoli go down but I've completely drained the kitchen gray tank and treated it with RV digest so I don't think the smell is coming from the tank. Only happens when we run the faucet. Strange thing is we don't get the same smell when we shower or run the bathroom sink. Wondering if it's an issue with the kitchen water lines or tank or if its just the water that is coming in from the park? We have an external water filter so just not sure what is going on. Has anyone else experienced this amd if so how did you make it stop?

[PSU Turf]

To rule out the tap water: Fill a glass with water from the kitchen tap. Does it smell? If no than the smell is coming from the drain.

What does it smell like? Is it possible something is caught in the trap? (broccoli)

[Skyliner]

Food particles washed down the sink which end up in the grey water tank can cause bad odors.

Recommend you fill and flush the tank several times and on last flush, leave a couple of gallons of water in it and dump a 1/3 gallon of ODOBAN (like the lavendar scented one best) down the drain and you should be good to go from here on out.

[asquared]

If it is coming from the fresh water line, try saint your lines with a 10% bleach water solution. Let that sit in your lines for a few hours and then drain and rinse thoroughly. You can use the same water to further vlesn your grey tank.

Also check your p traps. If you don't have p traps then I believe you have a valve that could be bad. This can allow odors to escape up through the drain.

A third possibility is the air vent is blocked by something ie mud daubers.

[Goferbroke]

We had the same problem a couple of weeks ago and found that the vent pipe from the tank to the roof had broken and left about 1/8" gap in the pipe. Draining water into the sink forced air and odors up through the pipe and through the crack causing the odor. Went to Home Depot and bought a vent line repair coupling made out of rubber with hose clamps and fixed in about 5 minutes.
For some reason when I posted the pic it rotated left 90*. Crack is on top of the T in the pipe

[RudysWorld]

There is an anti siphon valve in the drain line if you have a p trap which can go bad and cause fumes from gray tank to get into area under sink. for this you replace valve that is available at any hardware type store.
Also, there is a chemical reaction that happens sometimes in the hot water heater that will give you a rotten eggs smell. For this I think you drain and sanitize the lines to include HWH.