Adding Gray Water From One Tank To Another

[RognMar]

To Flap or not to Flap, that is the question.
Is there a flap valve on Gray tanks to prevent backflow.
23 Avenue 32rls, I had heard while Dry Camping/Boondocking. If your Gally grey tank is kinda getting full, [you could keep your main valve closed (Camco, Valtera) if you added to main sewer output hose fitting.]
Pull both Gray valve handles. Water from Gray 1 tank and Gray 2 tanks would combine.
I tried this in Gros Venture campground Dry Camping in the Tetons. Tank 1 and Tank 2 did not combine.
No familiar "Glug Glug Glug sound. Thought it might be a vapor lock. 15 minutes later no change. Tank sensors showed 2/3's in one and 1/3's in another. Any thoughts.

 

[BryanValRox]

To Flap or not to Flap, that is the question.
Is there a flap valve on Gray tanks to prevent backflow.
23 Avenue 32rls, I had heard while Dry Camping/Boondocking. If your Gally grey tank is kinda getting full, [you could keep your main valve closed (Camco, Valtera) if you added to main sewer output hose fitting.]
Pull both Gray valve handles. Water from Gray 1 tank and Gray 2 tanks would combine.
I tried this in Gros Venture campground Dry Camping in the Tetons. Tank 1 and Tank 2 did not combine.
No familiar "Glug Glug Glug sound. Thought it might be a vapor lock. 15 minutes later no change. Tank sensors showed 2/3's in one and 1/3's in another. Any thoughts.

Well, I am not aware of any flaps within the plumbing.
I would think that this technique would certainly depend on the tank and plumbing layout of a given rig.
I would also not put to much faith in the tank level sensor telling you the truth.

One thing that is for certain is that, water will always seek it own level.

 

[Lantley]

I have successfully combined grey and black tanks on my 390mp. I have tried to combine the grey tanks with less success.
I'm not sure both grey tanks are on the same plane. It's also a bit of a challenge to make water flow up hill.
I would trust the gauges to be accurate enough to determine your results one way or the other.