You can buy sponge prefilters made for the purpose. You can also make them yourself. A sponge intended for filter media, like one for an Aquaclear filter, just an example, can be cut to a size that works. You can use a knife or scissors to hollow out a bit of the middle, until it will slide onto the uptake tube.
I've seen a good suggestion, forget who posted it. He wets the sponge, freezes it, uses a drill to make the hole. If you have tools to do that, you'd get a nice even hole. But if you do not, the scissors or knife will work, just do a bit at a time, as you need it snug enough that it will stay in place.
I've made them about two inches square, and two or three inches long, with the hole in the middle, more or less. Don't make the hole go all the way through to the other end, or it defeats the purpose of having the prefilter.
You take it off and give it a good squeeze out in tank water every few days so it won't slow down the filter or get too clogged.
There are other sponges, from dept. stores, but many have anti fungal chemicals or soap in them. If you try one of those be sure it hasn't got anything in it that could harm fish. They also often are very fine pored, which means they will get clogged very quickly. So I think the filter sponge is a better bet. You know it is safe, and not so finely pored.