If I may, a few suggestions. Use a piece of vinyl pipe that fits over your skimmer drain pipe, do not use the barb fitting shown, it is too small for maximum flow. If you want to use a barb fitting use a barb fitting for larger diameter vinyl pipe, even if you have to use a coupling or a fitting to go to a larger size. If your pump is 3/4" output immediately bump up to 1" and continue with one inch until right before entering tank with returns. Reduce down to two 1/2" returns right before entering tank. If your not too impatient go out and buy a true "Y" fitting to use instead of a "T" fitting. A "T" fitting usually does a very lousy job of evenly splitting flow, so ball valves should really be used on each branch when splitting flow with a "T". Ball valves are not needed with a true "Y" which actually slits off like a capital "Y" not a lower case y. True "Y" are available at Farm Supply stores (for Irrigation Pipe", hot tub repair and supply stores where they are grouped together with "manifold pipes" and specialty houses which sell just PVC pipe and fittings. True "Y's" look like a capital Y not a lower case y. Regardless of your pipe size for efficiency you should always use pipe size a 1/4' to a 1/2" larger in diameter and reduce down at your "Y" or "T" or preferably just before entering tank. If your going to branch your line, go up a size, then down two sizes at your return nozzle. Think pi*r^2, the area of a circle. You want to deliver your water in a pipe at least 1/2 again more the area and you want your total of your split inflows to total up to your pump exit area. Example areas: 1/2"=0.785 square inches, 3/4"=1.767 square inches, 1"=3.1416 square inches, 1 1/2"= 7.069 square inches, 2"=12.566 square inches.
If you keep the same size pipe through out you will end up with probably 60-75% of pumps rating and not much velocity at your return exits. Lousy return rates is why so many people think they are getting 600 gph of flow through a 1" overflow. They try to base their unknown overflow on a pumps potential and not its actual return rate or even a calculated return rate. Bigger is really better when it comes to plumbing! Really! Want to borrow one of my hydrology books?
