I understand tea chest basses were quite popular with Liverpool skifflers - such as John Lennon's Silver Beatles - because the city was awash (figuratively speaking) in cheap throw-away boxes in which they shipped the tea. Thus I deduce that a determined bass player can use pretty much anything for a sound box.

I like the pictures on the link above, but a wash tub with a neck permanently afixed to it is going to be awkward to transport to gigs. I recently saw a portable wash tub bass used by a band here in Olympia, WA, USA (the Mud Bay jug band, to be precise.)

The neck (a broom handle) has a medium sized coat hook bolted into it. The tub has a hole in the middle of the bottom. The string has a washer tied on one end and a loop on the other. To assemble, the looped end of the string goes through the hole in the bottom of the washtub (Did I mention that the washer has to be larger than the hole in the bottom!?) The loop in the string hooks over the coat hook on the neck. Put the tub on the floor, stand the neck up, and pull back until the string is tight - ready to plunk!