Rat blockers are simple, robust devices that act as a one-way valve for rats. 4 inch rat blocker are inserted into a drain to prevent the movement of rats. Stop Rats! Effective Rat Prevention. Drain and Pipe Rat barrier. One-way flap maintains pipe flow but stops rats from entering. View all details. Over time, our rat blocker company developed highly efficient employees who are experts in their departments. It’s our mission to provide you with the best possible team to handle your rat problems. Our team knows the ins and outs of a rat infestation in any type of property. We understand property structure which makes it quicker for us to detect the root of rat infestation. With this, we make sure that your time isn’t wasted by constantly getting visited by pest control agencies. We aim for our rat blockers solution to withstand the test of time.