Within the Red Hat certification program, the RHCA is considered the most complete (and grueling) certification among the seven major Red Hat certifications. In fact, some equate the prestige of the RHCA to that of the Microsoft Certified Master and possibly the CCIE.
A plumbing fixture like a sink can not function properly without a sink vent. When a drain pipe drains it creates a negative pressure in the sink drain; the negative pressure will pull the water out of the p-trap of the sink that's draining and sewer gases can enter your home if a sink vent is not installed.
As long as the sink drain and its vent are connected in a straight line, the drain can serve as a wet vent for the toilet. This means, however, that if there's a blockage downstream of the sink, water can back up through the sink pipe. You can get a good idea of the plumbing configuration to which the sink is attached by noting which fixtures make the sink back up when they drain. They may also back up when other fixtures are draining.