Black tank flush access via Bathroom Sink Basin, Tab 400 BD, 2020

SweetHaven

I'm 99% sure the black water flush check valve is piped backwards.. It looks like I need to remove the complete sink housing to investigate.  I'm at a loss on how to remove the sink basin, which will allow me access to the two remaining screws directly behind the sink basin.  After I'm able to remove the white plastic housing I hope I can remove the plywood to gain access to the check valve.
Thank you for any help,
Sweet Haven

(Title edited for search purposes.  Moderator)

Denny16

Here is what the wall looks like with the sink removed.  Once you get this far, yiu can cut the two black flush tubes, and use a hose barb union to reconnect them the right way round, without removing the ply support bit.

The two white tubes marked with red arrows are the black tank flush lines.  Good luck.
cheers

SweetHaven

I found that by tilting the sink at a small angle from the closed position, I was able to get to the two hidden screws.  I then looked for that style valve online and found one that had a picture of the correct flow direction.  Mine was piped incorrectly.  Thank you for your feedback.  Your advice seems like the best practical approach.  A trip to the hardware store tomorrow and I'll be putting this problem behind me.  Thanks again.

ChrisFix

@SweetHaven
How did you know to look for this - what's the failure mode look like? Are you unable to get water to flow to the flush sprayer? 
Thanks!

Denny16

Chris, there isn’t a failed valve, it is just installed wrong way round, so water from the hose black tank flush connection is not getting through the valve. This is a one-way check valve, which only allow water to flow on direction.  There was a discussion on this last year or so, which showed a top view of the valve and the factory fix for this.
cheers