In two of our stalls when we built the first barn we installed drains. This was nearly 35 years ago, to date we have never had need to use the drains.
Flooring is concrete pavers over road-base with a four inch bed of sans to set the pavers then 1 inch stall mats. (this barn is just a 24 by 36 structure but has over 100,000 pounds of material in the flooring )
Bedding depends upon the horse (or animal) in the stall, the geldings get unwetted pelts mixed in heavily in the center of their stalls (primary bedding is medium flaked pine shavings), the mares get some dry pellets added in the perimeter. We have had one horse who was allergic to pine who was bedded on shredded straw …insert Expensive here (which was sort of pain in the butt as the volume of waste removed in that stall would equal that of three other head)
I can says that every veterinarian who has been here in the last three decades has commented on “your barns do not smell like urine”
Stalls are cleaned twice or more per day if the horses are stalled all day otherwise they are cleaned when they horses are put out (currently due to heat they out at night until about 10 or 11AM then stalled under their personal fans until evening)
While on this subject, after many years of not using our overhead fly spray system we started using it again (sucked up the cost to replace defective nozzles and get the system back to 100%)… Nearly zero flies now, at least 99% are gone. We had fallen back for a long time of buying the bottles of various fly sprays, then spray the horses Then this last winter we were reviewing costs with an intent of finding Where We could reduce the expense… fly sprays by the bottle are convenient but very expensive in the long run and with little relief for the horses.