I have frequent sewer, wet dog, swamp smell in my dishwasher and kitchen sink drains. What do I need to do to fix this problem? It is intermittent making it difficult to diagnose. I added an Oatey sure-vent to provide additional air and prevent siphoning p-trap. Dishwasher is to the left of my double sink. I do not have a garbage disposal. I do have an osmosis drinking water filter system where faucet is on top left of sink and drain hose is connected between the p-trap and air vent. See picture.
drain hose is connected between the p-trap and air vent.
So, that's a drain tube connection, if typical of RO system drains (can't be seen in the picture) not very well sealed at all, often just drilling a hole in a pipe and sticking in a small tube, directly into sewer gas.
It should be into the drain BEFORE the P-Trap, (like the dishwasher hose is) not AFTER it.
A leaky mechanical vent would also do it, but I infer that the one you have is basically new. A leak in the piping to the mechanical vent would be another potential leak point. But given the typical slap-dash approach to dealing with RO drainage I've seen, I'm betting on that being your gas leak. The drain tube certainly is a very different color the last bit going into the drain pipe.
Sterilize the drain piping with chlorine bleach in water 1/2 cup to 1 cup per gal of water. You could just pour this down the drain and let it sit for 20 min and then wash it out. This however might not come in contact with the upper part of the drain pipes.
You could try to fill the piping up to the air admittance pipe by temporarily removing the air admittance valve and inserting the right size of hose or a rag securely fastened to a rod or to a drain snake down the air admittance pipe to block the drain. Then pour the chlorine bleach solution down the drains so that the piping is filled with the diluted bleach. You might have to move the rag up and down at first to let the air out. The goal is to completely fill the piping with the bleach solution. Let sit for 20 min and then drain. After another 20 min rinse with water from the tap.