A viscometer (10) having a substantially horizontal reservoir (20) including a trap (24) for retaining a sample indefinitely in the reservoir (20). A substantially vertical measuring tube (12) disposed perpendicularly to the substantially horizontal reservoir (20) and depends substantially upwardly from the reservoir (20). A junction (30) interconnects the trap (24), a generally downwardly projecting fill tube (16), and a generally upwardly projecting vent tube (14).