If you are getting the 180 new the just order one predrilled. Otherwise drilling the back of the tank ,imo
, is better than a hob
overflow. However the bulkhead placement is not the determinign factor as to whether a tank will siphon out and overflow the sump in a power outage. This effect is prevented with the design of a standpipe. It is designed like an upside down U and the water level can only get as low as the bottom of the U in the worst case scenario. Check out www.dursostandpipes.com
that is the one I have. Also keep in mind tha return nozzles should be faily shallow, otherwise they could perform a siphon and suck out the water if for some reason the flow gets reversed when the power goes out. IMO
a check valve could be useful. They are a simple rubber flapper design that closes when the water flow reverses. Used in plumbing all the time and have a very low failure rate. It depends on how worried you are about a flood.