2007 5th wheel Chapparral 267RLS discharge confusion

[focstay]

Hello,
My newly purchased unit has a 1-1/2 discharge line which I suspect is the grey water.
The large dia. 4 inch or so, which disappears forward a few feet and is across from the toilet. This is likely the black water.
They join to one discharge.
On my last unit I emptied the grey water tank through the black tank.
I'm not sure how to do this as there is a pull valve on each line. It appears to empty each tank separately.
Can anyone clue me in?

[ChuckV1]

If you look at the handles one will be black and the
other gray. The small line/pipe is the gray water and
the larger is the black water. As the OP stated empty
black 1st and gray 2nd

[1492]

Moved from Forum Technical Support

[Old-Biscuit]

Hook up sewer hose to that 'common' 3" line

Open black tank 3" drain valve
When black tank is empty-----------use flush connection on side of rig to flush black tank.
Close drain valve

Open grey tank 1 1/2" drain valve
Drain grey tank
Close drain valve

Add some water back into black tank......2 full toilet bowls flush is good. Keeps bottom of tank wet

[ScottG]

Empty the black first and then open the valve to the grey to rinse the hose out.