I converted the #'s to spaces because then the TRIM function would convert multiple consecutive spaces into one space - I wasn't sure you'd always have 3 hashes as your delimiter.

So using SUBSTITUTE would convert:

1###2
Into

1   2
And then trim would make that:

1 2
And then the 2nd substitute would replace spaces with commas to make:

1,2
As for dragging the formula down rows - Excel has an inbuilt short-cut for this. If you put the formula at the top of the column you want it in then when the cell is selected there'll be a small black square at the bottom right-hand corner. If you double-click this square Excel will copy the formula down as far as there is data in the adjacent column.