This is what I use. I have two garden hoses. One is about 18" and the other is about 10' long. I use the short one when there's plenty of clearance under the gray water outlet. I use the long one to reach the bucket positioned downhill when the gray water outlet is too close to the ground. I run the long hose under the camper to a downhill location, and I simply coil the extra hose in the bottom of a 5 gallon "Homer" bucket.
A 1 1/2" to flex drain adapter is great for dump stations, but, if your gray tank is full on the campsite, you'll need to be very discrete using a black tank hose to dump gray water into a bucket or other container, because that could draw unwanted attention and concern from neighbors and rangers.
This is boilerplate that shows my adapter and other comments.
Drain your gray water regularly--3 or 4 times a weekend. A 12 gallon black tank is plenty for about 4 or 5 days if you're careful. But a 12 gallon gray water tank will fill up in a hurry. We start with about 25 gallons in the holding tank and 28 gallons in jugs in the truck bed. Do the math. That gray water has to go somewhere.
We camp near lakes a lot. That puts the gray water dump valve very close to the ground, so I can't get a bucket under it. I have a fitting that adapts from 1 1/2" to hose end, and I use a short length of garden hose into a 5 gallon bucket.
https://smile.amazon.com/Valterra-T0...y+water+adaptr PUPS have been draining gray water into buckets forever. Most don't have gray water holding tanks. You can dump the bucket on a happy tree (boondocking), or into a pit toilet (campground). But if you don't drain the gray water regularly, it will fill your shower.
Note that the garden hose adapter will block solids such as coffee grounds from flushing out of the pipe. So I leave some gray water in the tank to slosh about during the drive home to clean the tank, and then do the last dump without the adapter when I get home. That flushes out the solid residue from dishwashing. You can do this at a dump station, or because this is just sink water, on the ground or storm drain. I have a septic system with manhole covers at home, so I dump black water into the septic, and I can dump gray water residue into the septic, too. (You'll notice that all those tent campers dump dishwater on the ground, too.) But be discreet if you dump on the ground or storm drain at home, because someone may mistake your actions for dumping black water.
I have an outdoor kitchen, so my last step is to open the gray dump valve and run the garden hose straight down the outdoor sink drain to thoroughly flush out the gray tank.
Alternative plan:
If you want to dump your gray tank at a dump station, many create an adapter that fits a standard black-tank hose. Someone else’s illustration:
http://www.forestriverforums.com/forums/attachment.php?attachmentid=137941 (seen in this thread).
There are a number of similar designs. And these are great ideas!
My objection to this one is having to use separate dump hose for black and gray water and dealing with the optics of appearing to dump black water into a “bucket” at the campsite.
But you could also use this hose,
1 1/2 in. Discharge Hose Kit-66000-WYN1 - The Home Depot and two of these fittings:
https://www.zoro.com/lasco-adapter-p...Q&gclsrc=aw.ds with hose clamps. Cut a short length of hose for one and about 10’ of hose for the other, and you can use this at the campsite and/or the dump station. The sump-pump hose is cheap and can be stored in the side cubby of the trailer so as not to get contaminated by the black hose in the storage tube or bumper.
There are often several ways to achieve the same goals. Whichever works best for you...
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