You have to apply all the techniques you can find on the Internet to achieve the maximum transparency so the maze is clearly visible. It could be worth printing only the top part first and manually filling it with the soap to see if it's coming out transparent enough.
I used naturally colored Das Filament PETG at 220/70°C with the minimum fan speed set to 0 which effectively kept the fan off until it started printing the second half of the head.
Make sure to clean up any printing artifacts on the inside of the pump fitting. I ended up with a fair amount of "zits" which I scratched off with the sharp edge of my tweezers.