If you pick up coco coir (an inert medium for hydroponics when plants need a bit more rooting space) you can dump that sludge right over top to water whatever plant you have growing in it.

If it ends up getting kinda gross, take it outside and hose a bunch of water through it to rinse it, good to continue. But mostly it just causes the coir to break down a bit faster than it otherwise would, so this is basically like adding compost continuously.

Doesn’t work for every plant, but does work for a lot of them! I have potatoes in such a setup right now, and it’s pretty swanky.