Why not Just carry extra Cans/Plastic Containers (as and WHEN you need them!) I.e you'll probably only want then on extended Cruises....(saving space and weight when NOT needed ) Ofcourse They must be well secured.
I strap them down to deck mounted Pad eyes... and a LARGE!! diameter Jiggle Syphon pipe?
Cheaper...easier and less "stuff" to go Pete Tong.
I can empty each 25lite can in around a minute.... don't wait till you run out!
.... I do have a 225litre under deck Tank!