Drain Rat Stop

I have been having a problem with Rats in my loft. I was told that they often come up through drains into cavity walls and then into the loft space. There are metal rat stops available for purchase that go into the drain to stop rats getting in while waste can still flow in the other direction. These devices are very expensive for what they are and so I decided to make my own. Though it is true that a rat could possibly chew the plastic at least you know you then have a problem at that location and can purchase a stainless steel version without spending lots on a guess.

I designed this for a uk 100mm pipe.