In certain cities, restaurants can be fined thousands of dollars per day for having a damaged or improper grease trap. The reason for this is that grease or oils that find their way into the sewer system will eventually congeal and harden, causing serious clogging issues in the city’s wastewater system.
While your average residential home doesn’t typically produce anywhere near the same amount of grease as a restaurant, there is no “safe amount” of grease or oil that can be poured into a plumbing system. The very same problems that can cause a restaurant to go out of business can be found in household septic systems.
For that reason, no matter how tempted you are to pour just a little bacon grease down the drain along with hot water, it’s a very bad idea. Instead, wait until the grease cools, and then simply wipe or scrape it into your trash.