A mix of one third pearlite and two thirds potting soil is recommended. The pearlite is to improve drainage.
I've had the best luck with donut shops and bakeries, which have large 5 gallon buckets for donut cream, fruit, and other ingredients. Places that sell bulk foods may also have buckets from things like peanut butter, and places that sell sandwiches get buckets for their pickles.
Here are all the places I've gotten buckets in San Francisco. I recommend going to small local bakeries for a small number of buckets, and only going to baked good manufacturers if you need a lot.
Ultimate Cookie -- 100 buckets (assorted baking ingredients)
Gerhard Michler Fine European Desserts, retail location Jolt and Bolt -- 20 buckets
Prickly Pig Co -- 5 buckets donated by Claire!
Pan Lido -- 5 buckets
Burger King -- 4 buckets (pickles)
Rainbow Grocery -- 3 buckets (Rainbow usually has one or two whenever I ask their bulk section.)
Grand Mission Donuts & Bakery -- 2 buckets (Bavarian cream)
Pancho Villa -- 5 buckets (cream for their stuffed churros)
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