[travelin texans]

I believe his referral to "flushing" is actually the sewer hose connection, at least that's the way I'm reading it.
Still confused though as I never seen a fresh water drain with a sewer hose connection, talk about a mess & an accident waiting to happen. If it were me & this is the case I would not connect my sewer hose to it, but get a dedicated hose so no fresh water contamination could happen.
Not familiar with his flloorplan, but if there's a sink, kitchen, bath or shower, in the front of the rv & one in the rear, two tanks with two drains makes sense.