ok see if this makes any sense to you
the return chamber is on the right, the middle is for whatever you want to put in ie carbon, reactors, heaters or such. the left is for ro water for auto top
the top left is your mixing tank, top middle is for the refug and the top right is for the skimmer. the holes in the brace is for the drains from the main tank.
the three little tanks with lid are for your three part dosing.
how it works is
1)one drain feeds the skimmer chamber which will keep a water height of 9 inches, than is over flows into a two inch tunnel that feed into the reactor chamber
2) the second drain with a ball value will feed into the mixing tank, with the ball value open it will force the water to overflow in to the refug chamber. than after the refug it overflows in to the same tunnel as the skimmer to end up at the reactor chamber. with the ball value turned off, the mixing tank will be isolated from the remaining parts of the sumps and you will be able to drain that chamber with a ball value installed on the side of the sump. than add water and salt, wait for it to mix and turn the ball value will bring the refug and mixing chamber back in line
here is a top view of how the skimmer and refug overflow into the tunnel
hope that makes sense lol