That was the first time I'd ever ditched that much beer at one time and while not heartbreaking, it was certainly not a great day. At least I learned some lessons that I will hopefully not have to learn again.
My story begins on my next to last batch which was meant to be a Negra Modelo clone. I had saved some WLP 800 Pilsner yeast and added it to a starter in a 5L Erlenmeyer flask in my laundry room on top of the dryer. To show that no good deed goes unpunished, I had moved the starter from the kitchen where I'd had them set up for my 8 previous batches using the Erlenmeyer to the laundry room to get them sight and sound out of my wife's way. Unfortunately some time during that day she ran the dryer and the Erlenmeyer toppled off and broke into a million messy pieces.
Since I was in the process of brewing at the time I decided to just pitch some saved WLP 1056, California ale yeast and hope for the best with no starter.
Then on the same day I was brewing my last batch, an oatmeal stout, I siphoned the Negra Modelo into kegs and then washed some its yeast which was in the primary fermentation buckets with Miller Lite, poured off the trub and pitched that into the oatmeal stout.
The first keg of Negra Modelo turned out great right to the end of the keg and I finished it after about only 4 weeks. However, the second keg of NM which had been sitting in the keezer for weeks while I worked on the first one had a nasty taste to it when first tapped which didn't go away after a few days and many tossed pints. Thankfully I've never experienced that nastiness before and hopefully will never again, so down the drain it eventually went.
Since I had pitched the oatmeal stout on the washed leftover primary yeast from the NM I was thinking at least one of those kegs would likely have the same awful taste as the second keg of NM but I was wrong. Both of them had it because I must have mixed the washed yeast together at some point. So another 10 gallons goes down the drain.
It was time for me to thoroughly clean the heck out of everything anyway (keezer, kegs, taps, fermentation equipment, etc.) and also buy some fresh yeast so no permanent damage was done and I'll be better off in the long run. Still, 15 gallons sacrificed to the brew gods will hopefully meet my quota for quite some time.