Sorry about the glue thing, I forgot to tell you not to. I never glue mine so I can take it apart to clean and store it. If I have a drip I use a rubber band as a gasket.
To regulate the water level I just twist the end cap. So with the bulkhead on the edge and not in the center of the pipe, if I want the water level high, I put the drain hole at the top of the pipe. If I want it lower for overflow problems, I just twist it sideways till it stops overflowing. If I need to clean it or pull out some roots (tomatoes) I just pull it off. Simple solution and its worked great for two years. GPS is correct with the drain size, mine is roughly twice the size and I put a diverter on the
pump line so it sprayed back into the nutes and aerated them more.
Raking my brain for more, but mine is still in storage and apparently I'm getting old. Plus it's finals week for the master gardeners program I am taking. I will try to make a how to sheet on my systems when I get more time and put them on my web page.
You should be able to save your system by leaving a couple of inches on the 90s and using couplers. Might not be pretty, but it will work. Might just need new end caps if ya glued those.