Replacing sewage ejector pump and basin

[TomZ]

I installed an ejector pump when it died about a week after I closed on my cabin 26 years ago, and the pump is getting weak now. The sewage basin is outdoors, rusty steel, and is approximately 24" wide and 36" deep and is at least 40 years old. I'm replacing the basin because I'm concerned about it developing a leak and am thinking of using a Polyethylene basin. Due to proximity to a lake I have to lift about 20 ft. in elevation with an 1/2 HP pump to my septic system.

Living in Minnesota I worry about the sewage basin freezing but I have only had the 4" inlet PVC pipe freeze up once, and I thawed and applied heat tape.

I'm tempted to go with a 30" x 36" basin to cut down on pump cycles and to bury the tank as deep as possible to avoid a frozen pump/gray water.
I noticed the 4 inch inlet on most of the new basins are located quite a distance from the top of the basins. There are also basins without inlet holes and you can cut the inlet hole. The higher I cut the hole, the lower I can bury the sewage basin to help avoid freezing the basin and it would give me more capacity between pump cycles. The current old steel tank inlet is about 6 inches from the top of the basin. There is a partially buried even older steel tank 42"x ? in my yard that is 50+ years old and it's inlet is 2 inches from the top of the basin (although I have a feeling that that tank may have been used as a cistern).

Questions; Has anyone cut their own inlet hole and how close to the top of the basin can I cut the inlet hole?

I do not use a check valve due to possibility of freezing problems between the basin and the septic system(50ft) so I am putting about 8 gallons returns to the basin after each pump cycle and figured I did not have to worry about an air-lock. Is a vent hole needed in the pump outlet pipe?

Thanks for your help.

 

[houndzilla]

So for example, Liberty Pumps basins have flat square faces for just that. You cut a hole and insert a pipe grommet which effectively seals the inlet pipe going in.

As far as adjusting the inlet height I have no idea how that works with the engineering of a basin, I guess as long as your float system is highly adjustable I can't see this being a problem.