Use that soil. Seeds from unwanted plants, aka weeds, come from many sources, bird droppings, on the wind, on animals traveling through the garden. Those unwanted plants are going to be something that you will need to deal with forever, no one has ever completely eliminated them from anywhere.

Bindweed is persistent. Put the container and soil in a black plastic trash bag and place the bag in the sunniest spot you have for a week. The heat will kill anything.

Or spread the soil out on a driveway or a tarp and let it get totally dry.

I have done that, with bindweed and quack grass, and they grew in the black plastic bags, catecody99's problem is with what roots and seeds may be left in the soil, not with the plants parts pulled from the garden.