A method of detecting endotoxin in aqueous solution comprising: a) combining dried endotoxin-activatable clotting agent with a predetermined volume of aqueous sample in a compartment of a closed transparent assay container, wherein the dried endotoxin-activatable clotting agent is pre-introduced in the assay container before the combining with the aqueous sample, wherein the aqueous sample is received in the compartment through a reclosable access opening of the assay container, wherein the access opening of the assay container comprises a luer lock or a luer slip; b) manually manipulating the assay container to mix the dried endotoxin-activatable clotting agent with the predetermined volume of aqueous solution in the compartment to form an assay mixture, wherein the dried endotoxin-activatable clotting agent and aqueous sample are capable of forming a gel clot in the assay mixture in a predetermined period of time at ambient temperature when endotoxin is present in the aqueous sample in at least a preselected threshold concentration; c) mixing control standard endotoxin of known endotoxin concentration with a defined quantity of the dried endotoxin-activatable clotting agent in a transparent control container to form a positive control mixture, wherein the control standard endotoxin is added in a precalculated volume to form a concentration of the endotoxin in the positive control mixture that is effective for gel clot formation within the predetermined period of time; d) storing the assay container containing the assay mixture of step b) with the access opening closed and the positive control container containing the positive control mixture of step c) at an ambient temperature of from about 18°C to about 29°C for the predetermined period of time, wherein the assay container is left undisturbed during the predetermined period of time of the storing; e) inverting the assay container when the predetermined period of time ends and visually determining if any gel clot which is present at an upper end of the compartment remains at the upper end of the assay container for a preselected period of time; and f) inverting the control container when the predetermined period of time ends and visually checking for a gel clot to validate the results. a) combining dried endotoxin-activatable clotting agent with a predetermined volume of aqueous sample in a compartment of a closed transparent assay container, wherein the dried endotoxin-activatable clotting agent is pre-introduced in the assay container before the combining with the aqueous sample, wherein the aqueous sample is received in the compartment through a reclosable access opening of the assay container, wherein the access opening of the assay container comprises a luer lock or a luer slip; b) manually manipulating the assay container to mix the dried endotoxin-activatable clotting agent with the predetermined volume of aqueous solution in the compartment to form an assay mixture, wherein the dried endotoxin-activatable clotting agent and aqueous sample are capable of forming a gel clot in the assay mixture in a predetermined period of time at ambient temperature when endotoxin is present in the aqueous sample in at least a preselected threshold concentration; c) mixing control standard endotoxin of known endotoxin concentration with a defined quantity of the dried endotoxin-activatable clotting agent in a transparent control container to form a positive control mixture, wherein the control standard endotoxin is added in a precalculated volume to form a concentration of the endotoxin in the positive control mixture that is effective for gel clot formation within the predetermined period of time; d) storing the assay container containing the assay mixture of step b) with the access opening closed and the positive control container containing the positive control mixture of step c) at an ambient temperature of from about 18°C to about 29°C for the predetermined period of time, wherein the assay container is left undisturbed during the predetermined period of time of the storing; e) inverting the assay container when the predetermined period of time ends and visually determining if any gel clot which is present at an upper end of the compartment remains at the upper end of the assay container for a preselected period of time; and f) inverting the control container when the predetermined period of time ends and visually checking for a gel clot to validate the results.