I'm not sure i completely understand the way to countersink the drains
If you use a hole saw, mark the depth on the outside so you don't drill too deep. ( tape around the hole saw or a mark with a Magic Marker )
Drill the pilot hole ( 1/4" center hole ) then the outside bigger counterbore. Then the smaller diameter inside hole for the drain. If you allready have the smaller hole for the drain and don't have the center hole to guide the saw, the trick is to either clamp some scrap blocking behind the hole and drill a pilot hole through it to guide you or put the larger hole saw on the arbor and then the smaller diameter hole saw inside on the arbor. The smaller one will stick down past the bigger one and keep you centered in the hole.--Ed
BUSIA
32 foot, no flybridge, twin 350 (chevy) Crusaders, closed (freshwater) cooling, 1:1 Velvet drive transmissions.
Proud to be IBEW.