Solvent fumes linger about 12-18" from the floor. That's why your combustion air intake needs to be above that. Same way with a soak tank, your sides should be at least 12" taller that your solvent level. Doing so keeps the fumes from flowing over to the floor and keeps the working strength longer. For tight shops, a 30 gallon drum placed inside a 55 gallon drum gives you a safer and effective soaker. Any fumes that roll over the edge of the 30 go down to the 55. Get a 55 gallon drum dolly and you can easily roll it around the shop. You can occasionally roll it outside and blow some compressed air in the 55 and expel any unwanted fumes. Get the wheels that are raw steel. They act as a ground.