You may wish to hold the negative carrier horizontally in a tray of water, then by gentle movement you should find the top sheet either slides partially out, or with a gentle pull, it slides out.
Once you have one sheet out, turn the negative holder over so that the remaining sheet is facing upwards, otherwise the holder starts to sink with the remaining sheet heading towards the bottom of the tray with the emulsion side about to collide with the bottom of the tray.
I have the original version of the Stearman tank, and another version with the (I believe) current negative holder.