A fat-tailed gerbil's tank should be arranged from the substrate up, because this species lives in its digging layer more than on top of it. A duprasi spends much of the day below ground in a nest chamber, emerges to sand-bathe, forage, and chew, then digs again, so the layout questions are really about where the burrows will run, where the bath stays usable, and where food can be hidden without turning the whole tank into a larder.
The underground end: nest chamber and quiet ground
Set the fat-tailed gerbil's main resting place at one end of the tank by burying a wooden nest box or sturdy hide in the deepest part of the substrate, with its entrance at surface level. Keep that end free of heavy surface objects, water bottles, and baths, because weight above a burrow roof invites collapse, and keep the tank's quiet end away from doors and speakers in the room. A second small hide at the far end gives the duprasi an alternative rest stop after a sand bath, but the buried chamber is home, and during cleans it should be the last area disturbed and the first restored.
The sand bath corner, kept open and stable
Place the fat-tailed gerbil's sand bath at the opposite end of the tank from the nest, in a wide, heavy dish or a glass container the gerbil cannot tip, ideally sitting on a flat tile or low shelf so digging does not bury it within a day. Duprasi rely on sand to keep their unusually dense, soft coats degreased, and a healthy gerbil will visit the bath most evenings for a thorough roll.
Feeding through the substrate, water at a fixed point
Fat-tailed gerbils are desert foragers, so arrange feeding as a treasure hunt: scatter the seed and pellet portion through the surface substrate and a loose hay layer in the middle and bath-end thirds of the tank, and hide a few prized pieces inside cardboard tubes or a small digging pot. Keep one small bowl in a fixed spot for fresh vegetables so you can see what was eaten and remove leftovers before they are dragged underground to spoil. The water bottle belongs fixed to the tank wall above a tile or platform at the bath end, where drips land somewhere that is easy to dry, because a bottle dripping into burrow substrate makes a damp patch the gerbil will abandon.
Chewing, climbing, and surface enrichment
Spread the fat-tailed gerbil's enrichment along the surface it crosses between nest and bath: cardboard boxes and tubes for shredding, willow and applewood sticks, a cork bark piece to climb over, and a low, stable platform that gives a lookout point without any fall height worth worrying about. Duprasi are stocky and not athletic climbers, so keep levels low and landings soft, and anchor anything rigid so burrowing beneath it cannot bring it down. A solid-surface wheel suits some fat-tailed gerbils and is ignored by others; if yours runs, place it on a stand on a firm base at the bath end, never on loose substrate where it tips.
Letting the gerbil edit the layout
Expect a fat-tailed gerbil to rearrange whatever it can move, and treat that editing as information rather than mess. If the nest migrates to the bath end, the original chamber may be too warm, damp, or exposed; if the bath fills with stored seed, feeding is too concentrated in one place. Make your changes one at a time, in the gerbil's own direction of travel, and keep the broad pattern constant: buried quiet end, open bath end, foraging ground between.
Keeping the tank's zone plan noted in KinsLe with Family Sharing lets anyone in the household restore the duprasi's buried nest end and bath corner exactly after a clean.