I HAVE made an overflow with an old HOB
70?) .... but that requires cutting the tank!
I cut off a 2"x8" piece off the top of my back pane of glass. This allows me to inset the the HOB
into the back of the tank so it is lower than the water line (siliconed for water tightness). My return pump takes water from the sump into the tank, which overflows into the HOB
, and is piped back down to the sump (by gravity only - no pump needed).
This overflow works like a conventional hang-on-back overflow, but with no need of siphons (and no risk of flood from siphon failure).
I use 1.5" pipe to connect the HOB
to the sump, which allows me to build a compact Durso standpipe inside the HOB
for noise control. It is small enough to not intrude into the space where the media normally sits, so I can use the existing media basket to hold a sponge prefilter.
My current setup handles 700 gph
without problems. Looking at the "thickness" of the water flowing over the lip, I would guess that I can go to 1000 to 1500 before a flood.
This is my original post & pic: http://www.aquariumadvice.com/viewto...032&highlight=