I rarely camp with full hookup and my black tank requires emptying about a fifth (or less) time than my grey tank. Generally, we may fill 10-15 gallons of grey water per day and maybe a gallon or so of black depending on showers, hair washing, chile dinner, etc. It's a pain to break camp to find a dump station so I use this cap on my grey tank and carry a five gallon bucket with lid. It's very easy for me to empty grey tank into bucket a time or two and empty @ wash station, campsite toilet or elsewhere as needed without breaking camp.

I suppose I could do the same with a unified waste port, but then my bucket would be contaminated with blackwater effuse from the common port and I probably couldn't carry the bucket in my TV.

That's why I like them separate.

fred

What it looks like to me (admittedly uninformed Rookie):

1. Black water tank touches common port.

2. Common port is now contaminated.

3. Cap goes on common port.

4. Cap is now contaminated.

Is this not right?  If you then flush grey water through the cap's hose connection, you might reduce the contamination level, but it's still contaminated.  Or so it seems to me.