Sewage pit bubbles at bottom

[Beau Buzbee]

I have an empty plastic sewage pit that is bubbled at the bottom. It is raised in middle about .5-1”. I’m concerned about installing pump and then having the bubble depressed once water and waste enters pit causing my pump to be unsupported and pressure on my pvc and fittings. Any recommendations on how to level base of pit? Also, is silicone a good idea on top around gasket/lid to ensure I have a good seal?

 

[LLigetfa]

How many gallons is the pit and how deep? You could fill the pit with hot water and see if the bottom drops. If it does, I would expect it might stay down after the water cools.

A sewage pit is not usually pumped down as low as a ground water sump pit so once it is filled, the bottom of it should not move up and down. You could opt for stainless steel riser pipe if concerned that PCV will be stressed. Keep in mind that there is also motor torque stressing the pipe.

At one time I thought it was a good idea to place stones around my ground water sump pump to keep it from moving around. Turned out to be a bad idea. I had put too many stones in and the stones rubbed against the side of the pump motor, rubbing off the protective coating and the aluminum motor housing corroded resulting in failure. I wrapped protective tape on the replacement pump and rearranged the stones so as not to rub on the motor.

I've since replaced that pump and opted to use rubber pipe instead of plastic.

 

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[Beau Buzbee]

How many gallons is the pit and how deep? You could fill the pit with hot water and see if the bottom drops. If it does, I would expect it might stay down after the water cools.

A sewage pit is not usually pumped down as low as a ground water sump pit so once it is filled, the bottom of it should not move up and down. You could opt for stainless steel riser pipe if concerned that PCV will be stressed. Keep in mind that there is also motor torque stressing the pipe.

At one time I thought it was a good idea to place stones around my ground water sump pump to keep it from moving around. Turned out to be a bad idea. I had put too many stones in and the stones rubbed against the side of the pump motor, rubbing off the protective coating and the aluminum motor housing corroded resulting in failure. I wrapped protective tape on the replacement pump and rearranged the stones so as not to rub on the motor.

I've since replaced that pump and opted to use rubber pipe instead of plastic.

How many gallons is the pit and how deep? You could fill the pit with hot water and see if the bottom drops. If it does, I would expect it might stay down after the water cools.

A sewage pit is not usually pumped down as low as a ground water sump pit so once it is filled, the bottom of it should not move up and down. You could opt for stainless steel riser pipe if concerned that PCV will be stressed. Keep in mind that there is also motor torque stressing the pipe.

At one time I thought it was a good idea to place stones around my ground water sump pump to keep it from moving around. Turned out to be a bad idea. I had put too many stones in and the stones rubbed against the side of the pump motor, rubbing off the protective coating and the aluminum motor housing corroded resulting in failure. I wrapped protective tape on the replacement pump and rearranged the stones so as not to rub on the motor.

I've since replaced that pump and opted to use rubber pipe instead of plastic.

The pit is 18’ to the bottom of drain. Thanks for the tips!