Blank tanks

[Dsflorida]

I have a 2013 open range travel trailer the panel says black one and black two, on the outside there is only one black pull. Which one do I leave it on the panel. Also when I push the alert button on the black it says it’s 2/3 full but I have pulled the lever outside and drained it already. Not sure what I am doing wrong?

[opnspaces]

As valhalla360 states there might be a second tank. But then again there may not. Does the trailer have one or two toilets? One toilet I would assume one tank. Two toilets and there could be a second tank. Crawling under to look might be your best option.

Other thoughts. If one tank always reads 3/4 full it could be a faulty sensor (very common) or it could be the second tank that you haven't yet drained.

Is the trailer new to you? Have you ever drained anything out of the black tank or are you still learning?
If you did drain a tank did either gauge drop from reading something in the tank to reading empty after you dumped it?

[valhalla360]

We've had a few units that had 2 gray tanks (one for kitchen & one for bathroom). One had the two gray tanks plumbed together with on valve but the others had separate valves and the second one isn't aways obvious.

[valhalla360]

The gauges never work right, so don't worry. 

Crawl under and look for an extra valve.  They sometimes hide them.