The black tank drain pipe and valve are typically larger than the grey tank drain pipe and valve. If you have a black and grey tank draining from the same point it should look something like this but some trailers have the valves remote from the outlet and the valves have long cables to the handles.
2011 Rockwood Signature Ultra Lite 8293SS, 12K Equal-i-zer
2016 Ford F-250 XLT SuperCrew, 6.2L, 4x4, 6'9" bed, 3.73
2010 Rockwood Roo 23SS (2012 - 2014)
2009 Ford F-150 XLT SuperCrew, 5.4L, 4x4, 5'6" bed (2012 - 2016)