Final answer:
Used oil filters must be hot drained for at least 12 hours to remove all the residual oil. Hot draining involves heating the filters to a high temperature with the help of a hot water heater. The time required for hot draining depends on the Btu rating of the water heater.
Step-by-step explanation:
Used oil filters must be hot drained for at least 12 hours to remove all the residual oil. This is because oil filters contain residual oil that can contaminate the environment if not properly drained. Hot draining involves heating the used oil filters to a high temperature, which helps to liquefy the oil and make the draining process more effective.
Hot draining requires the use of a hot water heater, which typically has a heating capacity measured in British thermal units (Btu). The greater the Btu rating, the faster the oil filters can be drained. For example, if a hot water heater has a rating of 30,000 Btu per hour, it would take approximately an hour and 20 minutes to complete hot draining.