If you think about the layout of your 27FB, the solids enter the tank on the curbside and the dump valve is on the street side. As Pahaska says, plenty of water is the key. This is what works for me: If we are going to use the trailer for 4-5 days, I run the tank flusher with the dump valve closed (don't get distracted) to put enough water in the BW tank before we head out. The trip home allows the mix to slosh and blend. When I get home, I dump with the flusher running and then close the dump valve for 5-10 minutes to put a significant amount of water back in the tank and then dump again. The last of what drains out is clear. Then I dump the GW to rinse the slinky.
Air Safe Hitch, Reese Dual Cam 800#, Centramatics