Holding tanks

[RandandDoug]

Bought a used 2019 Keystone Avalanche 321RS.
All company specs I have seen show it having 1 black and 1 grey tank.
There are two grey Pulls and one black. The salesman and I did a fairly quick walkthrough, my 3rd rv, and he explained that there are 2 grey tanks, and the that was that.
I am out today familiarizing myself with the trailer, flushing tanks and stuff, and it seems as though the bathroom sink is plumbed into the black tank, not sure about the shower yet, will be going back out to run some water through that too.
Is anyone here familiar with that? Seems strange to me, but I can live with it. Just curious and all the places to call are of course closed for the weekend.
Thanks

[wildtoad]

Not uncommon for bathroom sink being plumbed to the black tank either due to ease of plumbing or to help assure sufficient water in the black to assure sufficient water to have things flow properly.

[agesilaus]

Dump some dye and water down the drains one at a time and see which valve shows the color

[ssthrd]

On my 2014 Laredo, there is a black (Right side) and a grey tank (Left side) between the frame rails directly under the toilet and the sink/shower. (Just repaired the grey 😞 ).

There is another grey under the galley sink.......... Not sure about the fresh water tank, but I assume it is beside the grey and on the left side.

The front tanks look to be the same size...........

Hope this helps. Good luck getting info from Keystone.

[work2much]

Pretty common for 5th wheels to have 2 grey tanks. One for the bath and one for the galley.