When removing the screw that holds the seat on, gently raise the seat while you unscrew it so that it stays in the metal tab. I lost 2 screws by not doing this. I think there's a gremlin down there somewhere that eats them. I was on concrete and never did find those screws
A great method however care has to be taken with your method and if i ever lose my big magnet i might just use itAnother way to magnatize a steel screwdriver is to wrap the shank with insulated wire, the tighter the wrap the better, and then momentarilly touch both ends of the wire to the posts of a car battery. A mean MOMENTARILLY...just a second or so. Not enough to melt the insulation off the wire!
HD even has a replacement screw for the seat to make it easy to remove by hand. About $20. I would also take that useful strap off and throw it in the trash.