Porous clay pots have been used in this way for a long time. Many irrigation systems delivering rainwater grows slimes and algae capable of blocking irrigation system drippers. Could a buried plastic PVC or PET drink bottle with a hole filed out to neatly jam a poly irrigation pipe into the head be recharged under pressure from a water tank and have as many pin holes as necessary to maintain a steady stream of moisture out into surrounding soil? As the holes clog up with algae the bottle could be exposed again and more holes added. The holes that have clogged would not totally stop the passage of moisture and eventually with enough clogged holes there would still be enough moisture leaving to support surrounding plants. Maybe putting heaps of pin holes in a bottle and filling the bottle with dispersive suspended clay might help speed up the process of setting up holes that release moisture for the plants if they want it but not streams flow that flood the plant. Has anyone else done this or got any suggestions? As the water tank empties the pressure will gradually reduce - how much of an impact would this have on these types of osmotic systems?