Dry hopping in a corny keg

Pour off the first few pints until you don't see any hop particles in the bottom of the glass and it should lose that flavor. You are more than likely just sucking up hop debris and drinking it.

 

There would be less hop debris if you had used a fine mesh nylon bag.

 

let it rest a few days days and try again. the dry hops make the beer "green" for the few few days, especially with Columbus dry hop. I have found the onion character more pronounced when I dry op and drink right away. hopefully this will subside for you. patience.

 

I have posted before on how to modify a dip tube and use that keg to dry hop in and then transfer that dry hopped beer (after cold crashing a few day) over to serving keg via CO2 push. I've had great results with this for a few reasons:

Rousing hops into suspension daily.
Maximal surface area contact of hops:beer when you lay the dry hop keg on its side.
Anaerobic conditions.

 

I use this stainless dry hopper and it's fucking great: http://www.stainlessbrewing.com/Dry-Hopper-with-twist-cap-currently-out-of-stock_p_155.html

 

That's exactly what I use as well! I also have a larger one for my boiling vessel, but use it instead when I drain my wort to the fermenter. Works great - catches most of the hop and break material, leaving very little sediment other than yeast when I'm finished fermenting. That also makes it great for harvesting the yeast.