A few comments:

1) I am not sure what benefit, if any, running it down and then back up would offer. The sippers at the bottom always have the most water pressure anyway due to the force of gravity on the water column in the tubes. There would be no need to put them first in line as a result.

2) I would suggest not having those two racks hooked up to the same water jug. That section where you run the tubing along the rafter appears to be higher than the water bucket, I'm not sure that's a good idea.

3) If your water source is small and only a few inches higher than your top sippers, they will never receive much pressure. Get that water bucket up a little higher compared to the top sippers.

That's all I can think of. Nice setup, and I love those gray rats. I have to get into some of those.

JonV