Yeah, that's a dribble but I don't understand something. That is the pump output pipe, the pressure side. I can understand the dribble but not sure how air would be getting into the filter. Unless somehow the air is getting in when the pump is off. In any case, you need to Unscrew the pipe adapter from the pump and looks like you'll have to cut the pipe to do this. You can get all the PVC parts at Home Depot, Lowes, etc. It looks like a 1.5" pipe so you'll need some 1.5" pipe, a 1.5" male pipe adapter, Purple Primer, PVC cement and teflon pipe tape. I also recommend getting a coupling you can disconnect in the future. You'll put that in a section of straight pipe right above the pump outlet. Talk to someone at the home center and they can set you up with all the right parts. Once you unscrew it, clean the threads on the pump the best you can. Looks like they used pipe dope when they screwed that one in. Use about 8 turns of teflon tape on the new adapter and screw it in. The nice part about adding that coupling is when you get it all back together and it leaks, loosen the coupling and screw in the adapter a little more.
Hope this helps.
Al