Simple new to Graystone Question on a 2011 33QB


Hello all, I want to use my stupid question card..
I'd rather be embarrassed by asking this than finding out the hard way- real time, the owners manual is generic to several models and i cant find the specific answers i need.

With regards to grey and black water tank draining, there are 2 sewer drain outlets on the left side(no doors) one towards the front and one towards the back.
There are 3 valve handles at the water station labeled 'Waste water' and 2 'grey water' valves, it does have a 1- 1/2 bathes.
My question is.. does one drain outlet empty the black tank and the other handle grey? if so which is which, it appears that the smaller diameter drain pipes seem to route to the front drain, so I assume the front is the grey tanks and the outlet in the rear is for the black tank? or could one of the grey tanks 'share' the black tank drain. When I open the black tank valve I dont want any surprises on which outlet drain it comes out. If someone could point me to a plumbing diagram for this unit that would be great.
My other question is I have located the black tank flush connection in the water station but there is another connection on the other side (door side) between the 2 doors also labeled 'sewer flush', are there really 2 flush connections??



Well-known member
Hi Keith,

My guess is that in your water station or Universal Docking Center (UDC), you have 3 handles: Gray #1 (front shower/sink), Gray #2 (kitchen), and Black (front commode). There's probably a fitting there for that Black tank.

The 1/2 bath commode and sink likely both empty into a 2nd black tank located in the rear, having a separate flush fitting and a separate valve handle and 3" sewer outlet.

It's very helpful to have a clear adapter on the end of your sewer outlet, along with a twist-on external gate valve. The clear adapter allows you to monitor what's coming out of the sewer outlet. The external gate valve allows you to close off the outlet before towing. Then when setting up, attach the hose before re-opening that valve. No surprises on your shoes.

With the clear adapter, you can easily test the gray valves by running the kitchen faucet with the Gray #2 (usually the middle) valve open to see if water runs out the front sewer outlet. You can do the same with the front bath sink faucet running while Gray #1 valve (usually the top) is open. And the same at the back with the 1/2 bath sink.

Clear adapter. There are simpler versions, but the one with backflush fitting and gate valve will help you to clear blockages that occur from time to time.

Twist-on external gate valve.

Hopefully someone with a Greystone 33QB can confirm my guesses.


Thanks a bunch!! I went and looked closer in the back and sure enuf, there was a valve handle for the tank in the back, which makes sense of the second flush, and now it all makes sense!! Thanks again.. (somewhat sheepishly, but much relieved!)