Jesus! You dont piss on the plant man!.........you piss in a bottle with a sugar solution..bacteria ferment the sugar and produce CO2 gas.The bottle can be outside of the cabinet with a tube linked to the inside. To see the gas being produced, one can place the free end of the tube into a glass of water and observe the bubbles burping out [slowley] . the principle is the same as a bong..to ensure no bacterial infections ..use conc' salt water in the glass!