Applying Filtering on NAT'd Packets

[Dani Tekeste <danitt10%yahoo.com@localhost>]

Hello, I was hoping I can get some help on this. 

I'm trying to block some packets which I have already applied NAT on but it 
does not seem to be working. Is there a way to filter packets after applying 
NAT??

Here is what I'm doing. 
nat pass on en0 from 192.168.10.31 to 192.168.10.180 -> 192.168.10.33

block drop out on en0 inet proto tcp from 192.168.10.33 port=55555 to 
192.168.10.180


Thank you,
Dani