The 2017 Waterway ProClean Plus cartridge filter base has a more versatile plumbing fittings for both the intake and discharge. The outside thread is a 2.5″ buttress thread, however it is also internally threaded for a 2″ FPT. The 2016 model only had the 2″ FPT. The pre 2015 models were also different plumbing fittings. The date of installation does not always determine which tank base you need, it is the date of manufacture that determines these issues.
The bases (pending year) are the same size for all the different size cartridges, only the lids change in size. Waterwayparts.com can assist you in choosing the correct replacement.Email us images of the tank you are trying to replace to sales@waterwayparts.com