Tanks without nooks and crannies for oil to accumulate in are best. If you have an irregular shape, put the skimmer where the largest amount of oil accumulates. Consider a means of directing oil toward the skimmer medium to improve removal efficiency. All skimmers work more efficiently in quiet water with a relatively thick oil layer. The greater the turbulence, the lower their efficiency due to emulsification.
Turbulence also affects the physical performance of a skimmer.
For example, a tube shaped medium may get kinked due to turbulence, which could cause damage or impair its drive mechanism. Mop types may require a tail pulley with its axle secured to the side of the tank. Belt types may be fitted with a tether or stabilizer bar assembly to resist twisting of the tail pulley. Disk and drum skimmers can handle only minor fluctuations, limited by the radius of the disk or drum. This dimension also determines the minimum usable depth.