The straight ammonium thiosulfate will clear, but not at the optimum pH for long life, at not the pH for adding hardener... Someone I know was using it straight, but developed problems with incomplete fixing with films and prints picking up pink or blue casts and fading over time... Sodium sulfite + acetic acid become sulfuric acid that is not affected by developer carryover...
For the vent, anything that can draw the air over the tray out will be a big plus, and an input vent that can equalize pressure in the room is good...
Steve K
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