Your local sewer plant has some great root starter! :)
When I was working at one of our sewer plants last week they had a potted tomato that had gotten broke from high winds in a storm.
I told them to stick it in another pot to root. They got creative and experimental.
They cut it in to 6 pieces. They put 2 in flasks with water from effluent (the clean but full of nutrient water that is discharged into the river). They put the other 4 in fresh potting soil.
They watered 2 one them with tap water and the other 2 with effluent water.
The tap water plants are alive but suffering. The soil and effluent water plants are already growing like gang busters. The 2 in flasks are full of large healthy roots!