I have several lengths of hose for varying conditions - location of sewer. Normally connected both hoses together towards the middle with the Y you have a pic of, and running a hose to the sewer, rather than running a hose from each drain to the sewer and using the Y there with a short piece of hose to the sewer. Your issue will be having everything run downhill, i have a couple of the plastic tray extensions that hold the pipe somewhat in a straight line, one for each leg off the drain and a slinky for the section from the Y to the sewer. I have a selection of 4x4 black I use for bracing and a piece of 2x8x10 I use to elevate the Y. (The old blocks I had for under the levelers and tongue jack on the old trailer, along with a few bags of the yellow lego leveler blacks.
2015 Georgetown 364TS, '14 Fiesta 5 spd w/Tandem Tow Dolly HDXL 8x10, & EZGO Customized Cart
'16 - 51 days camping so far, 19 more min planned; '15 - 56 days
2011 Flagstaff V-Lite 30WFKS '14 - 24, '13 - 33, '12 - 36, '11 - 29, '10 - 23