Drop this sieve into the drainage point of an ebb and flow tray and the bits never make it to your pipes. It is 24 x 11cm and suits the 1.1 x 1, the 2 x 0.8 and the 2 x 1 trays. When the water heads back to the tank after a shift, loose roots and leaf scraps get left behind in the mesh.
Skip it and that gunk drifts into the pump and clogs the flow. Fit it and every flood and drain cycle clears clean. A couple of quid of plastic that saves you stripping a blocked line on a wet Sunday. Slot it in, leave it be.