Desiring a quiet system but having little space to work with I replaced the simple standpipe in my existing acrylic overflow box with a hybrid standpipe derived from the Stockman and Hofer designs, but with a couple modifications made to add some new features. Notes on this standpipe build: 1. Per Ken Stockman's suggestion I dremeled a 1" x 1" square opening in the drain pipe to prevent blockages. [ref R. Durso's 180g - Ken Stockman Standpipe[/URL]. I made sure that at least the bottom edge of the hole was level. ] 2. First modification made was my replacement of the PVC end cap, used by both Stockman and Hofer, with a plug (i.e., "flush bushing") on top of the drain. I found that a 3/4" plug fits well inside a 1" drain pipe with just a minor amount of sanding. The 1/4" air hole is drilled into the top of this plug instead of the end cap. The main purpose of this end cap mod is to reduce the overall height of the standpipe, allowing the air hole to sit comforably below the rim of the overflow box. According to Hofer, this will function as an emergency drain if the water level rises above the hole: a full siphon is created along with a loud slurping sound to alert me of a problem. [ref Hofer Gurgle Buster[/URL]] 3. The secondary purpose for this end cap modification is to increase the upper range of adjustment for the bell, since the inserted plug has the same outer dimensions as the drain pipe. Completed hybrid standpipe with sliding bell adjusted to the bottom of its range. An end cap is so bulky it removes at least half of this adjustment range. Achieving the same adjustment range on an unmodded design would require extending the drain pipe higher - thus making it less useful as an emergency drain. 4. A third purpose for the end cap mod is to allow the bell to be removed from the top of the standpipe for cleaning without unscrewing a bulkhead or undoing a union. This is not possible with the Stockman and Hofer designs. 5. A fourth purpose for the end cap mod is to improve the capacity of the drain, at least compared to the HGB. The picture below is from the HGB construction page. Water flows into the top - note the obstruction caused by that huge end cap! 6. Second modification. I'm using an inverted bell to cover the drain pipe, per Ken Stockman's design. But I've inserted a 1/4" rigid air tube through the air hole - extending it down to just below the water line, per Hofer's design. That's what makes this standpipe a hybrid! This tube will be siliconed in place and then trimmed flush to the top of the plug once it's been adjusted. Completed and in place - it fits!