How big is the hole? BRS sells sch 80 bulkheads. Sch 80 is the same sizing as sch 40, just thicker and totally unnecessary for aquarium use. $100 worth of sch 80 is $7 worth of sch 40. Don't waste your money.
Here is all you need for the overflow in sch 40 parts.
Bulkhead ABS Slip x Thread (Slip on the Flange/Head side) - Bulk Reef Supply
Durso fully explained for getting to work in overflow compartment..
Durso Standpipes
#10 - 1¼ PVC End-Cap with vent hole.
#9 - Connector made of 1¼ PVC. Glue to Tee, Teflon taped top for snug fit with End-Cap.
#8 - 1¼ PVC Street-Ell. Trim the connector for a compact design to help fit into smaller overflow chambers. Glued into Tee fitting. This is the water intake for the standpipe. Water level would be expected to be around the middle of this fitting.
#7 - 1¼ PVC Tee. Do not glue this onto the standpipe. Use Teflon tape on the standpipe for a snug fit. This allows it to be removed for height adjustment or maintenance.
#6 - 1¼ PVC Pipe. Sized long enough to get the End-Cap just about equal to the upper rim of the display tank.
#5 - 1¼ PVC Coupling. The stand pipe and reducer bushing are glued to this part.
#4 - 1¼ to 1 inch reducer bushing.
#3 - Connector made of 1 inch PVC. This should be glued into the reducer bushing. If you have a slip bulkhead, this inserts directly into the bulkhead — use Teflon tape for snug fit into the bulkhead.
#2 - OPTIONAL: 1 Inch PVC Male adapter - only needed on threaded bulkheads. You may want to attach to connector with Teflon tape to allow for a quick yank removal from bulkhead. Use Teflon tape on threads before inserting into bulkhead.
#1 - Bulkhead. The opening at the bottom of your overflow chamber to allow water to drain out to the sump. This drawing shows a threaded bulkhead.
