Despite what I thought was very thorough searching before, I just now stumbled across two better deals for a 1/2 BBL keg with 4” and 1.5” TC ports:
The Compleat Winemaker has a lower starting cost and shipping to my zip code happens to be about $10 cheaper compared to ABS.
Schaefer Container Systems also had a price including shipping that was lower than ABS’s base price, an extremely fast response to my request for that quote, and multiple sizes of kegs with tri clover ports. Only the 1/2 BBL and 100 liter kegs are available with the 4” TC port, but there are a few variations of the 1/2 BBL available.
(EDIT: on closer look neither is an entirely fair comparison, as it appears the ABS option includes the 4” to 1.5” reducer and may even include the TC clamps, gaskets and end caps. ABS may be willing to sell just the shell for a comparable price to the options above, it would be worth asking)
But I apologize for derailing the thread. Getting back on topic:
For the asking price I’d certainly be interested in trying! My understanding is tartrates are precipitated tartaric acid so I would expect them to dissolve well in a PBW solution. If that wasn’t enough then line cleaner or another aggressive alkaline solution should take care of it.