Re: gray water lever vs. black water lever?
Hi SequoiaGal and welcome to the RVUSA Forum. Ken gave you an answer to this question in the Beginning RVing section of the forum. You only need to post your questions once and we will get back with answers as soon as possible.
The cardinal rule for dumping the holding tanks is "Dump the black first, then dump the gray to flush out the hose." That plus you should wait until the black tanks is at least 2/3d's full to ensure you get a good flow.
Like Ken said, if you can't see the pipes, it will be a matter of guessing. You should be able to find out which is which after your first trip to the dump station. Good luck and welcome to the wonderful world of RVing.