The two tanks are not connected. They each have their own dump valve, so it sounds like maybe you have a cable loose or broken? You should be able to drop the coroplast underbelly and see the valves and cables.

You do have two tanks and they are NOT connected ... one is for the kitchen and one for the bathroom.  There should be two handles, one for each grey tank and one handle for the single black tank ... all should be in the wet bay, but I am not as familiar with the 3401.  Do you have a single outlet pipe or two?  If you have a second dump connection, the handle might be up under the skirt on the frame immediately near the outlet.  We have a 4001LK with the rear kitchen and a 1/2 bath so we have two black and two grey and the second grey is very hard to find up under the skirt at the rear of the rig on the frame right next to the outlet.

@rog-paul 

I took the coroplast loose and found the black water valve and the functioning grey water valve but the non functioning valve is somewhere up under the floor.  I'm at a loss as to how to get to the non functioning valve.  I followed the cable as far as I could reach but to no avail.  Any suggestions?  

I have a single outlet pipe for combined sewer.  The valve is apparently on top of the tank.  I cannot see a way to access it.  I would appreciate any help you can provide.  

I do know that some tanks are stacked ... may not be a need to get to the valve end of the tank ... can you follow the cable to the handle end to pull it?

Matt, let’s start at the wet bay where the pull handles are located. Do you have 3 handles there? One should be for black, galley and grey. We have a 38RL which was predecessor to the 3401RL. If you don’t have three handles, do you have an open spot for a third handle?

And…reading your description, it may be the galley valve you’re missing. That tank is usually located in the frame underneath the kitchen island, again accessible through the underbelly. You should be able to follow the drain plumbing, at least in ours there are two pipes to the left and one to the right which goes to the galley tank. 

Here is a pic a member sent of a 2017 3401RL with all three handles in the wet bay.

Here is a pic of a 2021.  If there is no handle or nothing happens when you pull it, than I recommend a mobile tech off rvhelp.com 

@webberwj 

That is what mine looks like.  2 grey, 1 black.  The right grey is the one that won't  open.  I pretty sure it's for the shower and bathroom sink.  The valve feels like the working one when I operate but no release of water.  I don't know how to access the valve to see what's doing on.  I was hoping a Redwood rep. could tell me what to do?  

Thanks for your response.  Matt

How do you know there is water in it?  Is it backed up or just a sensor reading?

@webberwj 

That is a good question.  I considered that thinking the 2 tanks might be plumbed together.   It's not backing up to suggest it's full.  The gauges are errartic at best so I discount them.  It does show water in 1 of the 2 after I dumped. 

My guess is, the dump valve is working, but the tank is empty.  Try seeing if you can put water in it and then dump.  A member with the same floor plan said on his that the shower and kitchen sink goes into grey #1 (top grey handle) and the laundry connection and bathroom sink goes into #2 (bottom grey handle), however we do find that from rig to rig, they are not all plumbed or wired exactly the same ...  I normally put a water meter on the end of my hose and fill up the tanks from the inside when I clean them quarterly to keep the sensors working we use either Commando pods from Walmart or Camco TST Probe Sensor Cleaner from either Amazon or Camping World.  You put the cleaner in, fill up the tanks and let them set overnight.  We also have a Kleen Tank service done once a year.  Our sensors usually work pretty well.

After reading this string, it occurs to me that the sensors only read at 33% intervals. Has anyone changed sensors to read more granularly?