Look at Grassroots living soil pots. Then order a 30 rather then a 25. Yes you can throw all your soil into the pot. If its used you will want to amend it. Order some Craft Blend and Big 6 from Buildasoil.com. Put in 2 cups of Craft Blend mix well. Water in 2 teaspoons of Big6. Never water more than 5% water to soil. so in a 30 gallon pot, 1.5 gallons of water is the Max water at any one time. Once all nutrients are mixed in, plant clover. soon as clover has a nice bit of green on it, mow it and then drop in your clone/seedling.
Here is a pic of my living soil bed that has 7 year old soil in it. Several runs through it.
View attachment 1202572
If you want to know more about this type of grow or a journal I have one here:
https://www.thcfarmer.com/threads/multi-strain-bed-grow-looking-for-keepers.134092/