What is the procedural tactic employed in the senate to prevent a bill from coming to a vote?

The answer is "filibuster".

A filibuster means a method in politics where some or an individual from the parliament or congress starts a debate on a bill in order to prevent the voting and then prolongs it with lengthy debates and discourses. That is why sometimes this kind of method is referred to as "talking a bill to death" or "talking out a bill".