Black Tank Flush / 2 Black Tanks

Thanks to all for your responses. I appreciate your assistance. I will do some crawling around tonight and see what I can see.

I have two black tanks with separate flush systems on mine. If your flush system is the basic hose connection on the side of the trailer or in a water control station there is probably one connection for each tank to flush the tanks separately.

I imagine looking at your floor plan there is a forward sewer hose connection for 1 black and 2 grays and a rear sewer hose connection for the 2nd black. If you look on the side of the trailer about 2' or so above the tank level near that 2nd sewer connection you'll see what looks like a garden hose connection. That will be the water supply to the 2nd black tank flush.

The flush water connection will probably look like a 2nd city water connection.

Use a separate hose to flush tanks not your good fresh water hose. A cheap garden hose will work fine. Mines brown :) so I don't confuse them.

Good luck.

My guess is that if the two black tanks are located front and rear in the rig, there would be two separate flush systems with two separate water hose connections. If you only have one connection, then it likely only flushes the main bathroom tank.
I have seen Keystone models equipped with two black tanks and only one with flusher installed.
You will know for sure by testing the water flow as stated above.

If you can't get a definitive answer, then fully drain both black tanks. The close both black tank valves, run the flush for 2-3 minutes, turn it off, then open one black tank valve and see if water comes out. If so, let it drain completely, then open the other black tank valve and see if water comes out.
If there is no obvious black tank flush select switch then I would guess that it flushes both tanks at the same time.

I have no idea, but if you hook it up then open each valve you can see if water is coming out.