ᐅ Does the base of a drainage inspection chamber need to be sealed?

Hello everyone,

I am currently considering whether it would make sense to omit the bottom of a drainage inspection chamber and instead dig about 30–40 cm (12–16 inches) deeper to monitor the water level in that area. Is this generally advisable, or is a sealed bottom (which might also be waterproof) necessary?

Since I am already on the topic of drainage: Our builder installed the discharge pipes for the toilet (KG2000 - green) directly into the drainage filter layer (5/11 crushed stone). Is there no risk of pipe perforation without a sand bed? Although the sand bed would likely be washed away within the filter layer.
At another location, the rainwater pipes (KG2000 - green) are also laid without a sand bed on the drainage filter layer. However, in this case, a 16/22 gravel filter layer was used.

Best regards

For your information: I have decided to use an inspection chamber with a bottom. I am still considering the issue of rainwater pipes in gravel or above the drainage filter (16/22 mm (5/8/7/8 inches) uniformly graded).