aboard from Eastern PA.
We also have a 248 RKS. The front dump connection near the bathroom has both black and gray tanks. The color coded handles control the respective valves. The rear dump connection is gray water from the galley sink only.
To use the black tank rinser snake a water hose under the camper and hook to the rinse port inlet. I use a fresh water hose dedicated to dump operations. Open the black dump valve and turn on the water. You can close the dump valve and let the black tank fill with water but keep an eye on the level. You don't want a mess in the camper!
I black tank rinsed for the first time this past weekend (and only my second trip). I was amazed at the extra toilet paper that was flushed out. I have a clear elbow to connect between the sewer hose and camper drain.
You can find some great videos on how to use the rinser on YouTube.
While at home it won't hurt to hook up the rinser and check that the plumbing for it in the sink cabinet doesn't leak. And when winterizing later this year don't forget that line also needs to be blown out.
Sent from my LG-H810 using Tapatalk