An isolation device for use with a casing gas separator. The device incorporates multiple cups, some upward-facing and others downward-facing. The downward-facing cup or cups seal against an internal surface of the casing gas separator to divert flow into the annulus of the separator and enable the separation process. The upward-facing cup or cups hold a pressurized fluid when the device is being located within the casing. Upon reaching the upper ports of the casing gas separator, the fluid releases into the annulus, allowing an operator to determine the location of the device and accurately place it within the casing gas separator.