David,
Yesterday I visisted a local vendor that supplies culverts and highway construction materials.
In describing my design for a venturi style overflow tube for overflowing bottom water using a 3' plastic dual wall culvert as the oversleeve
upriser and 2' plastic dual wall culvert as the downriser. The price quotes I rcvd were;
36" diameter tube = $35.60 per foot ($712.00 for 20' length). 24" = 18.24 per foot ($364.80 for 20' length). I was going to connect a 36" Tee oriented on its side to the bottom of the 36" oversleeve up riser to act as the suction opening. The vendor told me that the Tees are very expensive - almost as much as a 20' length of same size tube ($712)! He said that they cut a round whole in a 36" tube and make a stub insert to accomplish the same thing much cheaper.
He also said that the HD in HDPE meant Heavy Duty. I kinda smiled to myself as I doubt HeavyDuty is a name a chemist would give to classify a plastic. I'm still sticking with High Density something or other.