We have found that a 3 foot fume hood for liquid waste collection (only) in teaching labs is a really excellent way of keeping vapors out of the lab (as they pour off) and not crowding the (second/working) fume hood that is used for procedures. Yes, you could move the now-poured-off liquid waste from the in-process hood but if 2 students are working in a 5 ft hood (typical) while others are trying to pour off waste, it gets tricky. It has helped us with compliance issues and training students on proper hazwaste handling procedures, so it's been worth it in our view. We don't have these in our research labs due to space constraints...