Check valves...

This is going to sound retarded, but I would install these before the "fill" valve right?

You can do it that way. Putting it between the fill valve and the bag would be better.

i like em. tank empties, no worries...

thanks..recently I had a line break, and I lost all my air...then my truck ate the road pretty hard...that's why I'm putting them in.

If your line brakes between the bag & valve set up there's not much you can do.Check valve can't be right at the bag,or you can't dump. You can use braided lines between the bag & valves so pretty failsafe!

^or hardline it.

Check valves can be right at the bag if you run dual port bags. You can use one port as an up and the other port as a dump that's all.