Okay. It might be easier in the long run to make a pipe out of a small PVC tube that goes into the drainage layer, then conceal it with some kind of natural vivarium item. The reason I say this is that your method of lifting up gravel each and every time you want to siphon water out could get unpleasant after a while.
I do not, however, know your setup as well as you do. If a standpipe like I just described won't work for you, you can disregard that part.