How to sort or uniq a live feed

I'm looking to sort and isolate IP from a tcpdump live feed. tcpdump -n -i tun0 "tcp[tcpflags] & (tcp-syn) != 0" | grep -E -o "([0-9]{1,3}[\.]){3}[0-9]{1,3} works just fine but when I try to add the uniqprogram it fails: tcpdump -n -i tun0 "tcp[tcpflags] & (tcp-syn) != 0" | grep -E -o "([0-9]{1,3}[\.]){3}[0-9]{1,3}" | uniq -u returns nothing. Same with sort -u. Any idea on how to fix this ?