i just capped it, what is that pipe for anyway?
i just put it on due to the pics.
it is for when your power goes out. The whole idea is to restart when the power turns on again. If the vent is capped, it will syphon all of the water out of the overflow.
The gurgling noise could be from a number of things but is probably because your down tube is syphoning too quiclky and pulling in air from the vent. Buy a ball valve ($2-$5) and put it on the lower end of your system. Use it to throttle down the syphoning speed.
Unplug your entire system to simmulate a power outage and then plug it all back in to check for restarts. There should be zero overflows (water on your floor) and 100% restarts without your help.