One kilogram can outweigh a ton
Generator category is normally a question of how many kilograms of hazardous waste a site produces in a month, and a laboratory rarely produces many. Acutely hazardous waste — the P-list, and residues and rinsate from those containers — is counted on a completely separate and far smaller scale, and exceeding a very small monthly quantity of it puts a site into the largest generator category outright, regardless of how little other waste it makes. A single bottle of an acutely hazardous reagent going out in a month can therefore change a laboratory's accumulation limits, training obligations, planning requirements and reporting. This is why the inventory matters more than the weight, and why "we hardly generate anything" is not an answer to the question of what category you are in.