It's not a full size towel, it's a smaller bath size.
(It's actually one that my gym hands out, and it accidentally made its way home in my bag a few years ago.)
It used to be white. Everything in that towel that's NOT white is crap that was in my water.
I wash this towel about every 3 days when I do this.

Anyway, you can see there is flow around the top of the basket.
The water that goes through the towel flows at a slower velocity than the water that goes around the towel.
I know this looks hard on the pump, but this is my 3rd year doing this. (I forgot my towel trick when I first made this post).
My pump doesn't seem to care.