Howdy!
We have a Cyclone toy hauler with two 3" dumps. The front is (black and gray tank) I use a Sewer Solution to dump it. The rear (gray water only) I use a garden hose to gravity dump it both are connented at the ground with a "Y" connection I made from PVC fittings from Lowes. I find using Sewer Solution and garden hose much more user friendly than having to use and clean 3" stinky slinky. Especially if I have a long run like were we are now and the sewer dump is at the rear of my 5er. I would hate to run 20 plus feet of 3" sewer hose let alone two sewer connections.
"Happy Trails"
Chiefneon