Attaching a sink to the underside of a countertop may not seem like the most stable way to hold it in place. If you use the right kind of glue, however, there is virtually no chance of the sink pulling away, even with an attached garbage disposal. Some under-mount sink systems don't even require glue, because the screws that hold the sink attach to the countertop. When glue is required, the recommended type is a quick-setting two-part epoxy. It may be supplied with the other fasteners and paraphernalia you need to mount the sink. Lift the countertop off the cabinet and turn it over.