I've used various kinds. Please use a clean one. You put water in, then use the pump to pressurize it. On a hot day, I go through upward of six gallons in keeping my sculptures damp, spraying every ten minutes or so. This is very important.
Water holds the sculpture together.
This is a specialized tool, essential for some tasks such as making sure my tall, narrow colums don't lean. Mine is 42 inches long, to span the whole base. I've carried to the building site, and for holding my tools so they don't get buried as I carve. Also useful for mixing slurry for pattycake sculptures. They're available in building-supply stores.