Bathroom sink backflows into Shower

I recently purchased a 2017 Torque t285. We were not having any drainage problems until I emptied the grey holding tanks.

I emptied the kitchen sink tank, and immediately, the sink quit draining. I bought a sink and shower plunger and it seems to have solved the problem.

The next day I drained the black water and bathroom grey water tank. The toilet and bathroom sink are draining fine but the shower quit draining right away. The bathroom sink will drain then backfill the shower. I'm not sure if there is a clog past where the shower and sink drains meet or if maybe there is check valve not working properly. I tried to use the plunger but the floor of the sink flexes too much for a good seal.

Any help is greatly appreciated. Thanks.

I think you have a clog after the shower/sink Y connection, but before the grey tank. I am thinking you might be able to run a standard plumbing snake down the line.

There are also nationwide mobile RV holding tank service companies with fiberoptic inspection and remediation capabilities. Here is a listing for one of these companies: https://kleentank.com/

wdk450 said:

I think you have a clog after the shower/sink Y connection, but before the grey tank. I am thinking you might be able to run a standard plumbing snake down the line.

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I thought the same but I've run a 6 foot snake into the drain without meeting any resistance. There was a trivial amount of hair in the P Trap but other than that the snake comes out clean.

I think Bill may be correct about a clog. If it was a venting problem, it would act different.

If it was mine and since the snake seems to not have worked, short of taking everything loose, I would find a drain camera to take a look at it.

Trying different things like forcing water from each end with a hose or making the end of the snake more blunt to help shove the obstruction out may help.

If all that fails, I always ask myself, “What would MacGyver have done?”

You can get these fiberoptic borescope cameras to hook to your smartphone pretty cheaply online, and can use them for other stuff like inspecting your suspension, looking behind your storage compartment wall, etc. Here is a link to an E-Bay search of these: https://www.ebay.com/sch/i.html?_fr...escope+camera&_sacat=0&LH_TitleDesc=0&_sop=15