The bottel and pipe(plastic bottel and garden hose) is for sucking in fresh air. i have a hole drilled in the wall straight through to the outside which i then put the hose through.. i have three small 12 volt computer fans built into the bottle and the hose goin in one end and i sealed it all well so there is no air leaks.. so when i switch on the fans it creates a vacume in the bottle which sucks in fresh air from outside all the time...its kinda like a mini air pump... works well as plants need plenty of co2 to survive and it cost me nothing to build... as i say again funds are very low...