NLHE - Slowplaying a big flop

I called preflop getting over 8-1 odds with small suited connectors. I immediately check bottom 2 pair on the flop, he bets pot $18 with obvious overpair, I smooth call, faking the flush draw and hoping he'll push on the turn. I guess he was scared of the possible straight, so I had to donk bet the river.

Stage #1408027875: Holdem No Limit $1 - 2009-05-05 23:38:54 (ET)
Table: JEFFREY DR (Real Money) Seat #8 is the dealer
Seat 8 - LIVEWIREDW ($63.25 in chips)
Seat 1 - JAFFA007 ($37.50 in chips)
Seat 2 - KODIAKZERO ($108.85 in chips)
Seat 3 - HARDLYEM ($106.60 in chips)
Seat 4 - MIKEDADUTCH ($164.55 in chips)
Seat 5 - PTW420 ($120.25 in chips)
Seat 6 - AMB_KOSH ($156.36 in chips)
Seat 7 - HOLA PAPI ($420.40 in chips)
JAFFA007 - Posts small blind $0.50
KODIAKZERO - Posts big blind $1
*** POCKET CARDS ***
Dealt to KODIAKZERO [6d 4d]
HARDLYEM - Raises $3 to $3
MIKEDADUTCH - Calls $3
PTW420 - Folds
AMB_KOSH - Calls $3
HOLA PAPI - Calls $3
LIVEWIREDW - Calls $3
JAFFA007 - Folds
KODIAKZERO - Calls $2
*** FLOP *** [4c 6c 9s]
KODIAKZERO - Checks
HARDLYEM - Bets $18.50
MIKEDADUTCH - Folds
AMB_KOSH - Folds
HOLA PAPI - Folds
LIVEWIREDW - Folds
KODIAKZERO - Calls $18.50
*** TURN *** [4c 6c 9s] [5s]
KODIAKZERO - Checks
HARDLYEM - Checks
*** RIVER *** [4c 6c 9s 5s] [Js]
KODIAKZERO - Bets $20
HARDLYEM - Calls $20
*** SHOW DOWN ***
KODIAKZERO - Shows [6d 4d] (Two Pair, sixes and fours)
HARDLYEM - Mucks
KODIAKZERO Collects $92 from main pot