Since you didn't mention "auto" top off, here's my solution for now. It does need a pump though - I would not really recommend gravity feed for top off. Even a float switch connected direct to ro/di output hose can fail.
Materials Needed:
5 gallon bucket
mini-jet pump
1/2" tubing
power strip
Setup Procedure:
1. Set bucket outside display stand
2. Attach hose to pump and put in bottom of bucket, put other end in sump above water line.
3. plug pump into power strip, plug power strip into wall ( I actually forgot this part. :eek2: )
4. Add ro/di water to bucket.
Now when you need to top off.. turn switch on, turn switch off. It's an upgrade to what I was doing which was lifting bucket and dumping direct into display. Too much work. Now I just top up bucket. Yeah! Someday I'll get my "auto" solution.