Overflow without durso?

[CStrickland]

The pump is a Pacific hydrostar fountain pump item # 68393. I got it at harbor freight. Max head lift is 11.5 FT. I figured this may be the case because Im under half head lift, so the flow is much more. Even at full 3/4 siphon I still needed the 1" 2nd drain running on gravity to match the flow.

No. Max head means on level ground it will push 650 and it won't pump ANY water at 11'. There's no way you're getting 650gph at 4' head from a $40 pump. Your flow is inconsistent because you don't have a valve on the drain, so you can't restrict it to create the full siphon. Instead, it is building pressure and then flushing.

You can test the flow of your set up by holding an empty container under the drain and timing hoe long it takes to fill. Like use a 1/2 gallon pitcher or whatev and then do the math to get how many gallons that would be in an hour (gph).

 

[neomarz]

My previous tank had one 1" drain on gravity straight down with only the elbow from the drain. The 2nd drain was a 3/4 full siphon with only the elbow at the bulkhead. Both bulkheads were at the top left and right corners of the tank. And i needed both to keep the sump from running low level. My new tank has 2 bottom drains with the 3/4 only using the same elbow at the bulkhead and tubing 2 feet to the sump tank. The new tank is using the same tubing as the old but cannot get the full siphon. Im gonna test the gph and will report back. thanks guys

 

[thegrun]

Add a gate valve on the primary drain and you can reduce the flow to get a full siphon. You are not delivering enough water to get a full siphon with the drain wide open. Add a valve, problem solved.