You are going to want to take the drain plug out of the cooler and put together ball valve in place of it.  I used the washer that came in the cooler to seal the inside and many brews later no leaks.  I had a pretty easy time putting together the ball valve at home depot before I got home to make sure it was all going to fit but your cooler is sure to differ than mine so it may take a little more time.  You can buy these already put together but at around $30 I figured I could put one together for less than $10 and a couple trips to Home Depot.

 

 

 

The braid is used to aid in filtering the wort from the grain when the mash is done and can be a little tricky to remove from the hose inside.  I used a hacksaw to cut both ends off of the line.  Then a little finessing to get the hose out.  Think of it like those Chinese finger traps, push the braid together and inch the hose out from inside.  Some have said that using some dish soap will aid in getting the braid off but I found a little patience goes a long way.

 

 

 

After you get the braid off you want to fold over the end a few times and clamp down with some pliers to get a closed end and clamp the other end to the barb on the inside of the cooler.

 

 

Done!  Now you just have to figure out what the hell you are going to do with this thing. 

Here are a few more pics

I just upgraded my mashtun and here are some pics of what I did.

 

Got a 70qt Coleman Extreme.  Though the red one did me just fine for 10gal big beers it was tight so here it is.

 

 

After removing the drain plug (white parts on the bottom) I got the parts together for the ballvalve.

 

 

Here you see the hole on the cooler and the 1/2 inch pipe fitting pushed through.

 

 

Valve installed

 

 

Used a hack saw to remove the ends off of the toilet supply line

 

 

Braid installed

 

 

Crimped end

 

Hope the pics help

Cheers