A biological sample collection system can include a sample collection vessel having a sample collection chamber with an opening configured to receive a biological sample into the sample collection chamber. The biological sample collection system can additionally include a selectively movable sleeve valve configured to associate with the opening of the sample collection chamber. The biological sample collection system can additionally include a sealing cap that is configured to associate with the selectively movable sleeve valve and with the sample collection vessel. The sealing cap can include a reagent chamber having reagent(s) stored therein, and when the sealing cap is associated with the sample collection vessel, the selectively movable sleeve valve opens, dispensing the reagent(s) into the sample collection chamber.