One way to avoid a common plumbing problem is to make sure never to flush anything but human waste and toilet paper down a toilet. Other things made of paper like tissues, paper towels, and the like do not dissolve the same way toilet paper does and can get stuck.
Do not pour grease or oil down any of your household drains. Put them in containers and place in the fridge until they are solid, then throw them away. If you pour them down the drain, they can solidify in cold pipes. These solid masses will clog your pipes and are very difficult to remove.
The clean out plug can sometimes be difficult to remove, and if you are having problems, there are two approaches to fixing this problem One way is to make the fitting looser with a hammer and chisel. The other option is chiseling through to clean out the plug.
If you install a new water heater, and you start to have a Slab leak detection from the pressure relief valve, you may need an expansion tank installed. The pressure increases when the functioning of the water heater is being performed properly. Therefore, with your new water heater, it may be necessary to have an expansion tank as well.