A syringe filter is a single-use filter cartridge. It is attached to the end of a syringe for use. Syringe filters may have Luer lock fittings, though not universally so. The use of a needle is optional; where desired it may be fitted to the end of the syringe filter. The fluid to be purified may be cleaned by drawing it up into the syringe through the filter, or by forcing the unfiltered fluid through the filter.