I don't think the pressure rating on a drum is anywhere near that. I think <5 lbs. Don't want anyone testing 20 lbs on a drum. I have seen drum expand rapidly and we ran. Thanks for the info for the chestnuts.
I'm confused. There is no pressure on the drum or bucket. The top is open and we are blowing bubble in water here. I have now idea what you are suggesting.
Maybe I didn't explain the concept well. Worm castings are a great source of beneficial microbes. I want to introduce these microbes to the biochar before using it to mix in containers or to amend holes dug for trees in the field. When aerobic microbes are fed and aerated, they multiply quickly. So, the idea of worm casting tea is to increase the population of microbes and then pour the tea into biochar. The water acts as a carrier to distribute the microbes through the biochar.
So, to brew worm casting tea, you add unsulfured molasses (or some other sugar source) to a bucket of water and add worm castings and then aerate the mix for about 24 hours (at temps less than about 70 degrees it may take longer). You can also brew it without aeration if you want a higher percentage of anaerobic microbes.
The PVC diffuser is just a device to create a high volume of bubbles and some churning of the tea. The pressure coming out of the air compressor is only 20 psi. That pushes air out of the holes drilled in the diffuser. The pressure in the bucket is immediately relieved as the bubbles rise and hit the surrounding air.
The pressure on the bucket or drum would be the equivalent of putting water in an open Tupperware container, placing it in the microwave, and bringing it to a full boil.
Or, perhaps I don't understand your concern....