MyFishEatYourFish;2915181; said:
i like the idea of going higher, just cause of the extra wiggle room and time between top offs. all support should go on the outside of the joint between the new sump and the old, it will make it much easier to seel.
If you use that sleeve design for the wall with the instructions I gave, you get the water pressure holding it together instead of trying to push it apart.
Either way works, but wouldn't you need to add a cross brace on that big of a sump if you went with the support on the outside?