Originally Posted by VatorMan
Pour some concrete down the tub drain. Leak will be gone !!
True, but he'll have to move the fish upstairs...
Only a few screws hold the cabinets to the walls and to each other. Just remove the cabinets that are under the drain.
You may be able to get away with a 1X1 hole, just enough to get a pipe wrench in there, Unscrew the drain from the pipe, reputty and replace drain if necessary. If not, assemble.