I pour about a gal of water in mine, it sits in the bottom, (not enuff for the pump to pick up) - the solids settle, and get trapped into it, - helping keep the solvent clean.
It also reduces the total amount of "solvent" required
Don't you have a lot of rust in the bottom of the tank from the water? One of my friends 'inadvertently' got water in his parts cleaner and after the tank floor developed a pinhole, he drained it and the tank floor looked like the hold of the Titanic.