Plumbers are mostly dealing with single-household water and sewer/septic systems, and not the nasty crap you get from a city drain when it’s overflowed from too much rain.
They also wash their clothes when they get off work, and don’t stick them (still wet and sewery) in tupperware for a year to rot and grow icky organisms.
I would have thought that, regardless of a bit of poop contamination (which wouldn’t faze me, but then I have an infant daughter), the fabric would have deteriorated and rotted after a year spent festering and damp in a container?
In the “old” days my wife and I rinsed soiled cloth diapers, (remember them).in the commode before putting them in a pail to be washed. Even then we used chlorine bleach to get rid of the stains and all.
There’s bacteria everywhere , the clothes only had to be washed.
Unfortunate that we weren’t told if the OP went on to develop a deadly fungal infection from the spores released from the items in the container… It is possible to inhale too many fungi spores , eg when turning the compost in the garden.