sink not draining

Question how many gray tanks does your trailer have?
I strongly caution you not to push anything through the cheap plumbing for fear of causing damage.
 
I may be missing something. What year/model trailer? How many sinks? Rooted to/from where?

As best I remember every trailer I've owned drained from the sink into the galley tank. Some only had one tank more recent ones had a specific galley tank. The drain comes out of the sink(s), goes into a P trap then on down into the tank. Have you pulled the P trap? If the trailer is very old and you run junk into the sink it's probably blocked. P trap removal also lets you isolate different sections of the drain and makes it much easier to run something through the line to check/clear it. DON'T start filling it with caustic liquids. It should be a short run and easy to check.

What is the in line air value? The vent?
 
One grey tank. Pulled pee trap, and pipes to sink. All were clear, w/ no blockage. Ran snake down from vent pipe into grey tank. Thought something was blocking grey tank connection. Found no blockage at entrance of grey tank. All pipes to sink are clear w/ no blockages. But water won't enter grey tank.
 
You will get better responses to your problem if members would know what year and model trailer you have. Not sure what valve you are talking about ... the Air Admittance Vent or does your trailer use a HepVo valve to replace the p-trap. We need more info so we can help.

In another post you say you have a 38 foot Montana. If so I do believe that you have another gray (galley) tank.
 
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^^^ What Danny said.

The symptoms you presented all point to a full galley gray tank. Crawl under your RV, look along the roadside frame rail, up near the bottom of the RV floor for that "illusive handle"... It's there somewhere, typically just behind the roadside rear tire or just forward of the roadside front tire....

Without knowing your trailer brand, floorplan/model number and year, it's impossible to help with any "certainty of the answer", but symptoms don't usually lie. Check for and find that "hidden dump valve handle" and your problems will "disappear down the drain".....
 
sink

Sorry. I have 38' 08 montana w/ rear living room. I didn't see another grey tank when I reinsulated underside, but will look for handle where you suggested. Monitor say grey tank is empty, but the can be wrong. I have in-line vent as well as exhaust pipe in kitchen. Was a black crappy one. I replaced it with Oatey Sure-Vent. Hope this answers all the ???s.
 
ALL of the 2008 Montana fifth wheels show a black tank capacity of 38 gallons and a gray tank capacity of 76 gallons. That means two 38 gallon gray tanks. Somewhere under your trailer is a pull handle for the galley tank. Usually the bathroom valves (1 gray/1 black) are located near the sewer outlet. The galley tank valve is located AFT of that location. On your "mid galley floorplan" I would suspect the galley gray tank valve to be just forward of (or between) the axles. Look for not only the valve "pull tee handle" but also look for evidence that there was a valve handle. It would be a small hole where the valve handle may have been. Sometimes a valve extension rod will vibrate off the valve screw post and fall to the pavement while towing.

There are two gray tanks on your trailer, every Montana built in 2008 shows a "double capacity gray volume" so that handle is there somewhere.

You can download the 2008 Montana brochure here: https://www.keystonerv.com/media/2470/montana-2008.pdf if you don't have a copy. All the specifications, by model number, are in the brochure.

Just as a "second guess type suggestion" have you removed the Oatley admittance valve that you installed? If it's not working properly, it may cause a "water lock" that would prevent the sink from draining. This is "very highly unlikely" but at this point, probably worth a try.
 
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The valve you are looking for will be underneath the large slideout ....it’s there or the handle is missing.
 

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