Mash Tun Tainted

Hello everyone, I have a Coleman Xtreme 70-Quart cooler, http://www.walmart.com/ip/Coleman-70-Quart-Xtreme-Cooler/4807332, that I converted into a mash tun. I've done several all grain batches from it but had a time in which it got away from me and spent grain sat in there longer than it should have post completion. After cleaning it all up and getting it sanitized I notice a bit of the plastic now is an off yellow/brown color. I've brewed a few batches since this and notice just a subtle off flavor in each beer. Is this possible that I've allowed the plastic walls in the cooler to absorb something from that old spent grain that now I've ruined the mash tun? My stainless steel braided cable does have a few rust spots on it and I utilize brass fittings/ball valve at the other end. I've considered getting a new mash tun and learning from this mistake but I want to make sure that this is an actual possibility before I chuck it. Thanks everyone!

I would definitely assume the plastic is slightly porous and could have absorbed the skunked grain smell. I would avoid brewing with rusted equipment and ultimately would replace the mash tun to avoid possibly ruining batches. If not replacing it is an option, maybe try soaking the cooler by filling with hot water and oxyclean.

My plastic buckets do the same thing. A 24 hour soak with OxyClean and 170F water usually does the trick.

Or PBW followed by a bleach/water soak. Rinse well with hot water. & don't forget to clean the fittings & even replace the rusted braid. Sanitize before storage & again before using it. That may likely get rid of the stank stuff.

You might also soak the cleaned mash tun in starsan for a few days to kill anything "brewing" in the dark corners that your cleaning regimin doesn't reach. Definitely replace any rusting parts. Stainless steel isn't supposed to rust, so try a different source for any rusted stainless.

Well that's a relief that possibly all it would need is a new braid and a good hot chemical soaking.