Yes. Rodents like rats are incredible swimmers. Their secretive nature and ability to slide their bodies through the tiniest cracks has made them the best adaptors and survivors. They use the same capabilities to enter the drainage system.
If there exist any smallest cracks in your plumbing system, then they easily make their way into the drains. Our sewers are something that comes last in our mind. Being below the ground, we rarely care about them until a problem such as overflowing drains, drain smells, gurgling sounds etc. It is vital to conduct regular inspections of your drainage system to prevent these problems plus pest infestation.
To block the entry of rats from drains, you can use rat blockers. Wonder what rat blockers are?