Black and Grey Tank Dumping

[CGHappy]

This is our 4th trailer and our first Montana. I thought I knew how to dump the black tank and flush, but the gauges inside are not showing empty. It actually looks fuller. I pulled the black tank and it seemed to empty. (i can hear it) then I hooked up the flush and ran it for awhile with the it open. but it didnt seem to drain? This is where I get stumped. is there something I am missing? now the grey tank seems fuller too. and it should be empty.

We have a 2015 3791RD.

[Walt & Vicki]

Make sure you dumped all the tanks. We have a grey tank valve towards the front and 1 more grey and the black behind the axles. When you flush make sure only the black tank valve is open.Hope this helps.

[twindman]

Get a clear 6-8 inch extension and attach it to the end of the hose that attaches to the trailer. Then you can see if anything is draining and how fast. While at it add a Valterra valve on the end of the sewer drain on the rig. Keep it closed unless draining - saves unexpected problems(!!) when removing the end cap.

[Arkware]

Wondering if your valve handles could be miss-labeled?
Not un-heard of...

[Montana Man]

Use a clear sewer line fitting at the drain. It is easier to know what is happening when you see it.

[Daryles]

Use a USB camera. https://www.walmart.com/ip/Waterproof-HD-2M-7mm-Endoscope-Lens-Mini-USB-Inspection-Camera-with-6-LED-Lights-Borescope-for-Android-Smartphone-PC-Lapt-op/924102324?wmlspartner=wlpa&selectedSellerId=9869&a did=22222222228083850308&wmlspartner=wmtlabs&wl0=& wl1=g&wl2=m&wl3=196367365898&wl4=pla-314984353131&wl5=9020674&wl6=&wl7=&wl8=&wl9=pla&wl 10=115780161&wl11=online&wl12=924102324&wl13=&veh= sem&gclid=Cj0KCQjwl6LoBRDqARIsABllMSYrmCF7yr5V2gJF P-5xNI9Krm5qbbPKEhgUV67HYDWBjtlJen9H88IaAjUgEALw_wcB