Drilled = 100% flood safe 
External Overflow = Not 100% flood safe 
 
Valid arguments for both, they both can fail if clogged obviously.   
 
But the External Overflow can also fail if it loses it's syphon when trying to restart after a power outtage. 
 
I regret having an external overflow, it's a constant fear of flooding (happened a few times).  I wont make that mistake for the next tank. 
 
Regarding the sump, you would want a sump from the start.  That's where you keep all the equipment (protein skimmer, heater, filter socks, media reactor, maybe a section for chaeto, etc.). 
		
	
		
		
		
		
			
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				Gary 
Tank was up for 7yrs and 10months.   Thanks Everyone! 
 
2016/2017 180Gallon Build Coming Soon...
			 
		
		
		
		
	
		
		
	
	
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