I've been recommending this check valve, part number 47245K37 from McMasterCarr, as I have been using it for quite a few months now without problems. The website describes it as follows:
" PVDF Body with Viton Diaphragm— For external applications requiring superior chemical and abrasion resistance. Temp. range is -70° to +250° F"
Well, this morning this check valve failed and my reservoir sucked vinegar from the cleansing bubbler back into itself. As you can imagine, the acid in the vinegar combined well with the base KOH solution.
Apologies to all that I have recommended this valve to that have used it, it was fine for me for many months until now.