We needed a mash tun to batch sparge with and wanted to do it as cheaply as possible - not to mention follow the KISS* principle. For full Instructions on how to use it visit Denny's Batch Sparge page.
We started out with a Coleman 50 qt cooler we picked up at walmart on an end of season sale for $10.00. 50 qts = 12.5 gallons = big enough to mash about 26 lbs of grain max. At least thats the most we did in it - and it was tight.
Step 1 should be to remove the lid by taking out the 4 screws from the hinges going into the lid. We put the screws back into the lid after freeing the hinges in case we ever wanted to reattach it.
I found that a piece of 1/2" plastic tubing fit exactly through the drain on the cooler making a wort tight seal. We used a 30" piece feeding about 2" through to the inside.
A side benefit of using the tubing on this model cooler is the way the handles attach we can pinch the tube under the handle when not draining, acting as a valve.
We attached a piece of stainless steel braid from a heavy duty washing machine hose to the end of the tube with a stainless hose clamp - tighten it just snug enough not to fall off but not so tight it compresses the hose.
Crimp off the end of the tube by folding it and crimping with pliars and its done - literally a half hour job.
* Keep it simple stupid!