I hope this is what you are loking for :
Since ancient times non laquered terracotta vases have been the trap of choice to catch Octopus.
here is an image of one used in tunisia but pretty much everywere they were quite similar:

Now on Pianeta mare i saw an italian using two terracotta plant pots one slightly smaller than the other and attaching them together from the open side with cement.
Than saw off the end of the small pot with a saw.
Tie to a weight so that it does not roll with the current and it's ready.
Two other things
The octopus will go in the trap by himself cause he will choose it as it's current lair . It will not leave the trap even when being hauled up as he will feel secure in it . It will feel so secure it's actually a problem getting it out ( pour some sweet water through the small hole on the big pot and it will jump out )
5 days i think that is a lot isn't like 1 day enough ?