Hops are a vital ingredient in most beers, but they can present a messy problem. We need them in the boil but really don’t want them in the fermentor. Whole-leaf hops become bulky as they absorb wort and break apart, while pellet hops turn into green sludge. Either way, they can easily clog a valve, a racking tube, a pump, or a counterflow chiller.
There are several standard ways to solve this problem. The most traditional is to whirlpool the wort at the end of the boil. This collects the hops and trub in the center of the kettle, keeping them away from the drain or racking tube. The downside is that the whirlpool needs time to work; otherwise, it leaves a fair amount of hops in the solution (especially with pellet hops). Also, super hoppy beers can overwhelm this technique.
Alternatively, you can use a filter, either on your racking tube or attached to the kettle drain. There are numerous commercial choices, such as the Bazooka Screen or the Hop Stopper, but you can also make a simple filter out of a copper scrubber. Any of these work reasonably well, although pellet hops can often clog them up. Cleaning the filter afterward is also a hassle.