the Patterson washer won't actually wash 12/16 paper, it is a fraction too short still, as far as washing a 16/20 print folded to fit you risk creasing and damaging the paper, especialy FB paper, until dry it can be delicate and easily damaged when wet, maybe you could use a developing tray modified by drilling several holes in the bottom the under a slowly running tap the fresh water goes in the top and drains from the bottom, slower, but if you use hypo clear not so bad, I have used such a tray myself and it works well, certainly the prints I washed in it, both FB and RC paper the prints are still as good today as when I made them 20 or more years ago, these days I use a Paterson washer, works a treat for me