These are nice tanks. I bought two for my aquaponic system and like them a lot. The material is thick and they are very well made. The description says they will not hold more than two-pounds of pressure, which is fine if you use them for their intended design, which is to dispense dry goods or liquids not under pressure. Five stars.But, being a hacker, I wanted to use these tanks as bio-filters for my aquaponic system. My water pump sends water to the bio-filter, the water passes through the bio-medium, and out the outflow pipe. Some pressure is involved, but not much. (I drilled holes in the tanks, inserted UniSeals in the holes, then pushed pipes through the Uni-Seals to make the in-flow and out-flow water lines. I put valves on the bottom drains to drain out solid waste that accumulates on the bottom of these tanks.) Then to make the lids more-pressure-tight, I removed the lids, then unscrewed the screws that hold the lid retainer ring to the tank. I removed the ring and put a bead of silicone caulk on the retainer ring, set it back in place, and screwed it back to the tank. Next, when my wife wasn't looking, I snatched two Silpat baking mats from the kitchen and made two gaskets, one for each tank. I put these gaskets on the lids and screwed the lids back into place. I lightly tapped the lids with a hammer to further tighten them. I turned on the pump, stood by watching for leaks but none appeared. My mod is working very well. I don't know exactly how much pressure is in the tanks, but it is certainly more than two pounds. All is well; a life without leaks is a good thing.(A good story, but it was my wife's idea to use the Silpat baking mats. I don't know what I would do without her.)