Why would RAB put poison back into the bucket?

[greenfirespike]

No: HPFGUIDX 137722



Why put poison back into the bucket?  What does RAB have to gain by 
replacing the poison?  Assuming that LV set up the Horcrux and then 
RAB comes along and takes the locket, I am left wondering
why leave 
it with the same protections as before?  Whoever took the locket left 
a note, a note written to LV, so why bother to replace the locket?

RAB gains entry into the cave, and manages to find the hidden lake.  
DD tells Harry that the concealment of the hidden doorway is somewhat 
rudimentary (paraphrasing here).  Then RAB crosses the lake, and 
drinks from the bucket.  RAB then manages to take real!locket and 
replaces it with fake!locket.  RAB must then refill the bucket with 
the poison that he/she just drank, cross the lake and put the boat 
back, then seal the wall up.  

Are we to assume that the poison in the bucket is a rudimentary a 
spell as the spell to hide the lake?  Perhaps it is not as strong as 
many (myself included) have given it credit for.  But assuming that 
the poison is very dark and very deadly, then RAB must have been a 
rather competent wizard to not only survive the poison, but be able 
to reproduce the same poison and place back into the bucket.  

Alternatively, if LV wants to get the locket back, does LV have to 
drink the poison?  And if not, then perhaps other dark wizards who 
can identify the poison can also manage to summon it away without 
drinking it. 

Greenfirespike