My Splatoon cosplay. I'm cosplaying as my inkling from Splatoon 2 for a convention coming up on Easter weekend. (Eventhough this is a Splatoon 1 ink tank design, I just prefer it better.)
You could also cheat by making a smaller tube that fits inside the bigger tube, so when you fill it with liquid, actually only the outermost area gets filled up.
I am kind surprised no one has made a Pi to cart adapter for older systems... Like a universal flash cart just use a Pi Zero and SD card and off to the races