No magic fix from the outside. Sealants will just get pushed out. You'll want to remove that outlet adapter, clean the threads, and reinstall it with Teflon tape or plumbers putty to form a nice seal. Biggest issue is what that adapter is connected to above (out the pic range) and if it can be twisted. If not, you'll have to cut PVC just to unscrew that thing. You can post more pics for us to see everything.