FYI for HC 380/381 owners (maybe others I don't know):
I was confused by how Keystone setup the drain lines for gray and black tanks but now I have it figured out.
For some crazy reason Keystone thought it would be a good idea to put the rear gray tank remote lever beside the black tank remote lever just behind the rear axle and next to the black tank drain.
The other gray tank remote lever is over 8' away and right next to the gray tank drain.
Now with that setup you would THINK that the rear gray tank would drain out the black tank drain line which would allow you to use the gray tank water to flush the line after the black tank was emptied (my old trailer was setup that way and many of my friends SOBs are setup that way). NOPE, the rear gray tank actually empties out the same line with the other gray tank!!! The only way to flush the black tank is using the black tank flush line (the water hose connection). If you don't have a water hose at the dump station or have setup to use your 12volt water pump you won't be flushing the black tank!!
Why Keystone thought it was a good idea to put the remote valve handle for the rear gray tank way back by the black tank line is beyond me. There is plenty of cable to put it up by the other gray tank handle..... For that matter why they thought it was a good idea to have separate drains to begin with is a bit of a mystery. I don't think there is any regulations forcing them to do so and it means you will have to run an extra hose with a "T" while camping! And to make matters worse why on earth would you put the handles right behind the rear tire? If you have a blowout those handles are history....makes no sense at all to me
maybe one of you has a good reason for it?