Red Sea ReefCan 18L

The ReefCans utilize the most unused dimension in your system’s cabinet, which is height, resulting in more RO water for less valuable floor space.

The ReefCan can fit in the gap beside your sump even in Red Sea's Reefer 170 & 200 models
Can be easily connected to any ATO system
It can probably slide in nicely behind cabinet
The ReefCans have a transparent plastic body with an embedded water scale, so you can see exactly how much water you have left
The front opening is positioned so you can easily fill up the reservoir without moving it.
In addition, you will no longer need to fiddle with any tubes or cables, as there is a second opening at the rear just for this.
While suitable for most ATO systems, the ReefCan is specifically designed to hold the ReefATO+ syphon breaker. Once you set up the cables, you won’t need to disconnect them except for an occasional pump maintenance.