Just remember that once you get through the floor upstairs there is going to be about a 2 ft space before you hit the top plate of the 1st floor. Make sure your flex bit goes in perfectly straight or you will come out the ceiling and that is never a fun thing. The best thing to do is explain to the customer the risk that are involved in doing a wallfish like that. I've done hundreds of them and only messed up one time but I still tell the customer what can happen. Lots of times they will decide they don't even want it. Take your time and be carefull. Good luck
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