Limiting holes in glass is always a good thing. The tank will be stronger, and there is no need for expensive and time consuming tempering. Swiss cheese bottoms add $1,000.00 to a big custom tank if you include the drilling cost, tempering, thicker glass, extra valves and related plumbing. The liability of extra holes when it comes to leaks is another consideration.
I used to follow the trend of drilling holes everywhere including the eurobrace, but now I just run the return lines over the top and hide them with rock and or aragocrete. You add a bit of friction loss, but you save a small fortune and gain peace of mind when it comes to leaking and breakage.
There are some cases, such as island tanks that may require all of the plumbing to go through the bottom for aesthetic reasons. A two in one or three in one bulkhead would come in handy for these applications.
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