Chinook RV

New to the forum, Chinooks and RV's in general. We have had our concourse out on a couple short excursion's so far for learning experience before the cold weather hits.
I was adding water to the gray tank through the kitchen sink to fill it up a bit to practice draining the tanks & testing the electric valves before they were full of more "dirty" liquid.
After a several gallons of water from a bucket in the sink the draining slowed considerably, and started hearing gurgling, looked in the shower and water started backing up into the shower. (the tank was nearly empty when I started) The shower did drain but pretty slowly, still hearing gurgles.
I snaked the vent, I estimate I got all the way to the last elbow before the gray tank but not around that last ninety (didn't want to push too hard).
Looking at the plumbing diagram for the 2000 concourse in the reference section it looks like the only place it could be plugged is right at the entrance to the gray tank.
I see the shower 'p' trap in front of the rear bumper, does anyone know if the 'p' trap is glued or can it be unscrewed? May try to snake it from there if removable. Has anyone ever tried taking that off?
Ideas?
Is this a common problem with Chinooks?

Thanks in advance!

I believe everything on the input side of the tank is glue, but don't quote me on that.

I never pour that much water down the sink at once. I would try to push a snake down the shower P trap if that can be taken off easily. It is probably hair from shower, or oil/grease/slime from the kitchen sink. If you don't really need the flow capacity ({that is, 99% of the time it drains reasonably well), I would not work too hard on this. The tanks are small anyway, and the water pump is small. It is not like you are hooking the rig up to a 2 inch water line and use a commercial sprayer to jet the dirty dishes in the sink.

Have you tried a plunger on the shower drain? That's where I'd start ...

It's good that you did this test, as I would most definitely want it to be corrected. Resolving issues on the road is always a much bigger pain compared to doing it in your driveway, and any problem involving water/black/grey is potentially a large concern. My fresh water system flows nearly as much as a residential system, so proper drainage is mandatory.

Was your dump valve open? If not, I'd have it open while doing these tests.

Good luck. Let us know what you find.

On my 2000 Concourse the p-trap is glued. I had it freeze one winter and cracked, causing a slight leak, and when I repaired it, I had to cut it apart.

You could also have a slow drain if any part of the vent pipe going to the roof is blocked. I had a large wasp nest in the top of mine when I bought it, and that blocked most of the airflow (removing the top vent cap worked to remove it, but half the stupid thing broke and fell down the pipe, of course!). Only really noticed when pouring lots of water down the drain, or taking a shower.

If you really want to tackle this, you can use plunger like Scott suggest. Take a look at the plumbing diagram, and block all the possible vents. That means if you going at it at the bathroom drain, you need to plug up the kitchen sinks,the bathroom sink, and the vent (which may connects to the black tank so make sure the valve on the toilet and black dump valve are good). Do it on all the routes. Unfortunately, it is a lot easier to flow air than water, so you may want to use water jet to blast down the drain. The bathroom drain is one of easiest one to work with since it is the lowest drain in the whole system.