I think an aspirator pump should be the main vacuum source in a clandestine laboratory. To save water, or if your water pressure is low, you can construct a recirculating pumping station. This station has been completely redesigned since the first edition, and this units performance is truly outstanding. Details of this pump are shown below.
You'll still need a source of running water to keep the unit cool and flush out condensed solvents as the unit runs. It works quite well, however, and the pump can provide a higher pressure than most any municipal water supply. Use a 5 gallon can, plastic pail, or something similar to house the system. The overflow should have a fitting allowing the attachment of a one-inch or larger drain hose or the unit can be placed in a sink or bathtub. The pump is of the jet pump-type variety, and should be in the range of 1/3 to 1/2 horsepower. Units made for hot tubs and small swimming pools are also satisfactory; just be sure to check the rated pressure. The pump should provide a pressure of at least 20 psi, but 30 to 40 is much better. Their pressure is usually rated in "feet of head". Multiply feet of head by 0.4335 to convert to psi. The use of submersible pumps is not recommended as they raise the temperature of the water, and quickly reduce the vacuum. One pump can usually power two aspirators. The intakes to these aspirators can be connected with a tee for increased pumping speed, or they can be used independently. Increased pumping speed is especially needed when evaporating large quantities of volatile material. As with all aspirator pumps, the colder the water, the higher the vacuum. Adding ice to the reservoir greatly increases the vacuum.
This unit will outperform most any municipal water supply. With 30 psi, it approaches the vacuum of many mechanical pumps. It can handle solvents and other corrosive vapors easily. It can also function out in the country where water pressure is low or otherwise unreliable. The pail should not seal up air-tight. Leave a small space around the aspirator outlet to allow air to enter. The unit will not drain properly without an air inlet.
The baffle is important. It keeps bubbly, aerated water from being sucked up by the pump, which otherwise seriously would affect performance. Use one half of a lid to the can as baffle, and secure it permanently with silicone.
