Off flavor from two different kegs...?

So I recently got two used corny kegs, about 3 months apart, both from the same place. I cleaned them both very thoroughly - soap, rinse, pbw, rinse, rinse, etc. I also changed all of the o-rings on both of them. I have a new 5lb C02 tank and a new 5ft picnic tap (I think it's food grade PVC) that came with the kit.

I kegged a pumpkin ale back in October, and it always tasted off to me. It seemed like there was this slightly sweet finish to the beer. It was a residual taste that would kind of come in late, maybe a little in the aftertaste as well. My first thought was that maybe I hadn't cleaned the keg as well as I had thought and some soda flavor was still coming through. My other thought was that it was my first attempt at a pumpkin ale, so I figured that maybe the recipe needed more hops or something. The taste bothered me to the point that I set up a taste test. One glass of beer that went through the picnic tap, and another glass of beer that I scooped out of the keg with a measuring cup. The test was inconclusive. I thought maybe the scooped beer didn't have as much of the flavor, but the difference was minimal enough for me to think it was possibly all in my head.

so...

I put filtered H20 in the 2nd keg to make club soda. I was troubled to find that this water also has a very similar airy sweet finish like the beer did. It's really hard to describe the flavor. You wouldn't try it and say "hey, this water is sweet", it's more of a perception of sweetness. And it's not just me who tastes it - the wife does as well.

The only constants between the two kegs have been that I'm using the same CO2 tank, same C02 line, and same picnic tap. The CO2 itself was actually different because I had to get the tank refilled before carbing up the H20 keg. I did get the tank filled at the same place though - but I'm not worried about that because the place specializes in setting up draft systems for restaurants, so the CO2 should be fine.

soooo...

From what I've gathered from this forum - the taste probably isn't coming from the C02 itself, but I have to ask - does CO2 have an inherent flavor?

Also, is it possible for the C02 tubing to be imparting a flavor?

I'm thinking the picnic tap is the most likely culprit at this point, but even after pouring out half a cup of beer or water that's been sitting in the line, I feel like I can still taste the off flavor. Can an off flavor be imparted just by having the drink pass through the tubing as it's served?

Any help/ideas would be great!

Did you clean and sanitize the beer line and tap?

Replace the plastic tubing to rule it out. But maybe it was a diet soda keg and your dip tube might have dried soda syrup inside and it's giving it that fake sweetness? That's all I could come up with. Pull the dip tube and look inside. Good luck

More detail on how you actually cleaned...did you do a PBW soak or just rinse? If soak, how long? Did you use hot water? Did you remove the posts and allow them, and the poppets, to also soak in hot water?

My general procedure for a newly acquired keg is to completely disassemble it, throw out all the o-rings and put the lid, poppets, relief valve, and posts in the bottom of the keg and fill it to the brim with super hot water and PBW (or oxiclean) for 24+ hrs. Never had a problem.

Hm - I don't think I cleaned and sanitized the beer line and tap in between the two kegs. I think I just rinsed it off and assumed any beer flavor would wash out after the first few cups of carbonated water...

I cleaned the dip tube with a dip tube brush before putting the beer in the keg.

Gritsak - my cleaning methods were the same as yours. Overnight soak in PBW with all keg parts in keg.

I guess first step now would be to thoroughly clean the beer line and try again?

I'd clean the gas line too. I know I have one myself that took a small shot (like backwash) from a primed keg, and I do not want the off flavor (chance of) to get into anything. It may be more of a pain, but if you are trying to nail it down, that might be a place.

I'm starting to think it's definitely the liquid line. Poured out the water that had been sitting in the line for a few days and tasted it, then tasted water that hadn't been sitting in the line, and the water that had been in the tube had a very strong off-taste, but the other water didn't. I guess the weird sweetness that I was getting was coming from the plastic tubing. About to upgrade the line anyway.