I have the Thetford, not sure if it is 27 or 35 gallon, but it does have 4 wheels and is towable. You just drop the handle over the hitchball and drag it to the dump station. In my opinion, it is mandatory to be towable, because it is hard to move when it has 30 or 35 gallons of water in it, especially if you have gravel site or roads.
2010 Rockwood 8280WS Fifth Wheel
2013 F350 Crew Cab SRW, Standard Bed PS Diesel
Reese Airborne Pin Box, Reese 16K Manual Slider
Camped 28 Days in 2012, 23 Days in 2013, 29 Days in 2014, 30 Days in 2015, 9 Days in 2016