drain backing up and flushing

[zrogst]

The water level will not stay constant in this system and it's driving me insane. Already been called out for emergency visits twice because the tank is overflowing while sump runs dry. Water level in the overflow box rises, flushes, and silencers whistle.

setup:
Large tank upstairs, with external built-in overflow box going into two 1" drains. Currently setup with stand pipes and Maggie mufflers. Both drains travel via spa flex under the tank through the wall and to the basement where they exit the wall and are plumbed to schedule 40 hard pipe and end in filter sock chamber of sump.

The overflow is level (checked with level)
Total drain line distance is around 40-50'
One of the two drains appears to backup and flush, the other can handle normal water volume.
The return pump is choked with ball valve, and this flush occurs even at VERY low return volumes.
90s and 45s exist only at the wall exit and around sump no more then 3 per drain.

Today I cut open the dry wall and sliced BOTH returns at four points and shoved a pipe snake both directions through the drains. Unfortunately, I did not find an obstruction where I expected to.

Please offer troubleshooting suggestions this drain is infuriating.

 

[Arthur1]

What diameter is the drain line? To sum it all up as there are different variables that come into play when experiencing the flushing effect, it has to do with the ratio of water and air flow.

 

[Steve Atkins]

Does any of the flexible piping travel up hill, in the direction of water flow, at any point? This can cause an air lock. Ideally you would not have anything running flat either as I have seen this start to give trouble after a few years of operation (due to gradual build-up).

Steve

 

[TangingOut]

Try running without the maggie muffler. If that works, then the breather hole on the muffler needs to be widen. Drill open the hole in increments until you get a stable water level. This fixed my flushing overflow, although it never completely backed up.

 

[zachfishman]

If your drains terminate underwater, raise them up above water and see if that helps any.

 

[Icefire]

having more than a few feet of horizontal drain is asking for trouble unless your pvc line are 2-3".

You will get air lock and you loose the advantage of gravity.

I would use 2-3" pvc or ABS in the basement and would install some anti-syphon or a vent to prevent it from surging. Also you need to have a good slope

What is the gph to the display