I do water all my plantings from bottom and with the DE I usually keep a bit water on the tray all the time. The stuff that I use may not be the real DE or exactly like the one sold in U.S., but it should work the same way.
For my tomato seeds I used a plastic seedling tray with one piece 20 cell insert. I filled all except one of the cells with the gravel and I use the empty one to pour water on the bottom and via it I can see how much water there is.
This is how my babies look now
(Clicking the photo should open it bigger)
Sari