Keeping P.E.T. Bootles clean

I use PET bottles to bottle my brew.I have used them for 7-8 brews each.I use Chlorinated trisodium Phosphate to sterilize them .In the last few brews I have been getting about 4-5 bottles per brew that are off and taste foul.I was wondering if the plastic is getting harder to clean with age.I'm getting obssessive about sanitation but it still keeps happening.Any clues???

I'm not all that familiar with TSP, but isn't is a cleaner and not a sanitizer? If so, that could be why you are getting the bad flavors. Not all cleaners will sanitize, meaning that after you clean with TSP, there could still be some little crawling microscopic nasties in your bottles that are lovingly multiplying in your brew.

What I do know about TSP is that you need to rinse it, and rinse it well. How well are you doing that?

Chrlorinated TSP, aka Sani-brew, is a good cleaner/ sterilizer. My thoughts on your bottling problem is that you are a) not using a strong enough mix b) not letting it soak for long enough or c) not rinsing properly. Mix the stuff stronger than the instructions, soak for 20 minutes, and then rinse each bottle with a small amount of water 3 times.

I use the same stuff, and if I'm feeling lazy, I'll make up about a cup of solution, super concentrated, and pour into a bottle. Using rubber gloves, I shake the bottle around with one hand on top. Then I transfer the solution into the next bottle, and rinse the first. It's probably not the best way, but it's reasonably fast and easy, and I haven't had any bad bottles so far.

Are you rinsing your bottles as soon as they are empty? ie, are you sure all the old gunk is out when you are bottling?

I rinse out bottles after drinking always.What I do is make a bucket full off mix and wash bottle in it.I've started not rinse it straight away so it has longer to work on the nasties.The mix is pretty strong cause it smells like chlorine and burns your skin.The last two brews I have done like this but they are too new to try them.Also used a bottle brush in a cordless drill to clean off any residue on the last one then gave it a strong blast with TSP.