float valve in sump through glass

[Critter]

I know for the large bulkheads you use diamond bit hole saws, but how do you drill out the holes for a bulkhead on a float valve.. I think its like 1/2 inch or so? This would be on a sump that is currently in use.

Thanks

 

[SeaWeed89]

harbor freight has that size. or you could use a dremel with a tile bit i also think harbor has a strait diamond bits.