Bits of root and grit wash off the pots and head for your pump. Not with this in the way. We sit the cone at the tray drain point and it strains the muck out as the water leaves. The shape does the work, catching debris on its slope. A rubber sealing ring comes with it for a dry joint. It is a small part, 3.5cm each way.
The thread is 3/4 inch, so a matching tap winds straight on. That tap holds the cone down and meters the flow either way. No nut in the box, mind, so add one to fit your tray. One fitting doing the filtering and the flow control keeps the drain end clear.