While excavating for making a drywell, I found an old concrete prob 1000 gal./4000 liter septic tank in my back yard. Putting 2 and 2 together from property records and looking inside it, it was apparently emptied and sealed in 1960. Opened it up yesterday to 55 year old air which smelled--not too bad, pretty much like a cave smell. There is about 2inches/5cm of darkish mud/muck on the bottom.
I'm considering using it for non-potable rainwater catchment, thus might like to clean it out. Just wondering what--if any--pathogens I should be afraid of after 56 years of non-use, what techniques I might use to clean it, and sundry other advice.
I wouldn't be worried about any pathogens beyond your typical soil dwellers. you can easily get a pump to do some surface irrigation, and as long as it's not going to sprinklers the sediment will start flowing out too. This could also be a handy mixing tank for some compost tea...
Anything worth doing well is worth doing poorly first. Just look at this tiny ad: