Water Returning to Pit through Air Lock Relief Hole

I've got a new Zoeller 1/2 HP pump running fine, accompanied by a Watch Dog battery backup, both connected to separate outflow pipe that Y inside the pit, with a check valve about 18 inches about the pit lid. Problem seems to be that this time of year when ground is still saturated from spring thaw and early spring storms team up, the two pumps can't keep up with the inflow. But the problem's compounded by the amount of water that is pumped into the pit out of the air lock relief hole I drilled in the pipe inside the pit, instead of carrying it past the check valve and on out of the house.
Pump must send water straight up about 8 feet, then horizontally (virtually no slope down, but none up either) about 15" before exiting the house.
My relief hole is only 1/8", but again, it seems to be returning a large percentage of what the pump is trying to remove! Meantime, I've put tape and a clamp over the relief hole to give the pump a leg up, while the monsoon outdoors continues.
Ideas of flaws in my setup?

I'm not familiar with your backup system, but others I have installed required their own check valve. If each pump did not have it's own, one pump could push water backwards through out the other.

When you say it cannot keep up, are you saying that your pit is overflowing or ??

cacher_chick said:

I'm not familiar with your backup system, but others I have installed required their own check valve. If each pump did not have it's own, one pump could push water backwards through out the other.

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You nailed it! I had only a single check valve installed, above the Y, so my main pump was sending a good percentage of its outflow right back into the pit through the air lock hole in the backup pump's half of the Y.
Since the backup's controller has been malfunctioning of late, I've removed the backup from the system entirely until I replace it, eliminated the Y and now my Zoeller 1/2HP pump can completely empty the pit fast than it refills.

When you say it cannot keep up, are you saying that your pit is overflowing or ??

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Apparently, my good luck has been that the top of the drain pipes feeding the pit are at or just above the current water table, so the pit is NOT overflowing. But another day's heavy rain like the last two days' worth and that would have changed for the worse.

Thanks for the good answer!

1/8" is quite large of a hole. The best method is a stainless steel cotter pin set in from the inside and the legs bent out on the outside. Makes the hole smaller and self cleaning.

Closing the hole is possible too. Some think its not needed.