Ok after ready some websites I think I have figured it out. If you look at the image below you can see where the main blue feed comes up. The first tee branches off into the DI unit (blue cap)which has a tap on the other end. The 2nd tee branches off to the RO unit (white cap) and the tank(yellow line). The RO chamber has a white line with a tap on the end.
So 2 chambers, 2 seperate taps.
From what I have read DI water tastes bad so it makes sense that they designed it this way. Also RO wastes more water than DI. But seeing as neither really matter and if you run RO water through the DI chamber then you can go much longer before recharging/replacing the resin. (again from what I've read tonight)
So my thought is this. Switch the locations of the RO & DI chambers. This will allow me to run from the feed (blue line) into the RO chamber and the tank (1st tee). That way I still have my 3.2 Gal of stored prefiltered water.
Remove the tap from the outout of the RO and run it into the tee attached to the DI chamber. Cap the other end of the tee and attach my tap to the output of the DI unit.
This as far as my basic plumbing skills can figure out, will give me nice RO/DI water.
Am I correct in this assesment?? <<--- IGNORE THIS QUESTION
OK NM I am dumb. There I admit it. The RO is the BIG chamber before the 2 smaller ones. The 2nd small chamber is just a 2nd inline carbon filter to improve taste. So unless I'm worried about how the fishies think my water tastes, take water from the DI tap.
They really should provide better instructions with these things. I actually had to find a website to show how to hook the hoses up as the leaflet that came with it showed some parts and had a black and white image of the unit assembled. Thats helpful. LOL