Step 1: The Whole Thing All at Once
The blue storage box holds forty litres, because it was made for my 12 x 16 inch prints, but you could change that to suit your needs.
The holes in the spray bar are the same size as those in your bathroom shower head.
The syphon tube pipe is one inch (25mm) in diameter. The spray bar is half an inch (12mm) in diameter. Dimensions are not critical, as long as it empties faster than it fills up.
The hose on the bath tap feeds the spray bar pipe, which is plugged at one end to force the water through the tiny holes along its length. Rotate the spray bar pipe in its clips to get the aim right. The tank fills. The loaded prints are kept apart by the plastic fingers from an old print drying rack. The heavy chemicals leach out of the prints, then sink to the bottom of the water. The syphon tube, about one inch (25mm) above the tank floor, fills as the water level in the tank rises. Eventually it overflows into the attached airtight drain hose. The bottom end of this hose must be below the bottom of the tank (my bath is curved, which makes a gap underneath; you could use blocks). The syphon cycle starts by itself, gravity fed. The tank empties, the syphon action is broken as the air gets in, then the whole thing starts again.
It's in the bath because 40 litres of water is heavy. Any leaks or accidents won't flood your floor (keep the bath drain clear).