Sorry, I should have been more clear, this is not for a constant (on-demand) feed. I currently have a reservoir and ATO on each tank so they are set. This setup is just for producing the RO water and serving as a mixing station for salt water.
The 30g will be the main RO reservoir. One of the 15g will be what I use to top off my ATO reservoirs in each tank (I can move the 15g containers fairly easily). One of the 15g will be used for my water changes, I only need about 15g for water changes at a time.
That make it any clearer?