Backflow valve with pump or without

The main argument of our project management for a flap with pump function is our air-water heat pump with integrated ventilation installed in the basement. This is expected to generate a significant amount of condensate, which could not drain in case of backflow.

Does this change anything for you in terms of the decision, or are you still "anti-pump" and pro "standard flap"?

I would like to join the question or rather ask an additional question on the same topic:
If I have a toilet in the basement (foul water), then according to DIN regulations I need an electric backflow flap. Is that correct or is a mechanical flap also sufficient?

Background:
The street in front of our house is on a slope. The sewer line for wastewater runs from east to west past our house. The height difference between the shaft in the east and the shaft in front of our house is about 1.50 m and then slopes further downward. The street level in front of our house is about 30 cm lower than the planned house. The exact location and height of the pipes is not yet known.

Today an indemnity waiver to be signed came by email from our house builder in case we decide against this electric Pumpfix flap. Sure, they have to do that, but it gives the whole thing a somewhat different undertone.

Today we received a liability waiver to sign by email from our house builder, in case we decide against this electric Pumpfix flap. Of course, they have to do that, but it gives the whole thing a somewhat different undertone.

Liability waiver for possible consequences regarding the pump? Yes, but that does not change what was previously discussed or the risk assessment. It probably just reads differently now, pushed plainly to the point. But in that sense, your entire house is full of liability waivers, since you don't do some things everywhere for cost/design reasons. Insurances are also sold that way... with the implied assumption that something could happen. You can then insure it or live with the previously assessed risk, if there should actually be any significant one at all. But I understand you... when you read it so directly—

Liability exemption for possible consequences regarding the pump?

yes exactly, so in the sense of "in the event of backflow, the condensate from the heat pump and the wastewater from the water softening system can no longer drain and flood the basement"

I don't know how many bathtubs come out of both devices daily

The "risk" has not increased, it just reads as more likely now when you see the text in front of you. I would rely on what is described here.