Backwater (check) valve for small house pipes (2" / 50mm)

This is not designed to be watertight and prevent all backflow, but rather to severely limit the backflow. Good enough for my needs, whoever wants to understand them - please read the long explanation below.

Please mind when printing that this thing is potentially subjected to high temperatures and hazardous substances! So either make sure you don't use any of the above where it is, and/or create it from the right materials (PETG-grade and higher resistance to acids and heat), and make sure you know what you're doing and monitor the installation once you install! I take no responsibility for any misuses.

Size

2" drain pipes don't have a standard internal diameter. I've measured my own and got the info from the average found on the internet (which says for ~50mm PVC pipes the internal diameter would be 46.4mm). The size of the pipe insert is 46.2mm, please measure your pipe and scale accordingly when printing.

Printing

There are 2 versions, whole valve and valve with cutouts. Which one to use - depends on your expected water flow against the weight of the valve (for PETG - 19g for the whole valve at 100% infill, 10g for cutouts version).
Originally intended 100% infill for both, to have enough weight. However, looks like even the 10g weight of the lighter version might be an overkill, so:
In case you'd like an even lighter one than the one with cutouts - please print the whole valve with non-100% infill, and it'll become lighter, especially in the water. But do not make it lighter than water, it's functionally incorrect if you expect any water to be on the outside!
Use a piece of PETG filament for the hinge.

Why I made it (the long explanation)

I have a very long straight drain pipe from the kitchen into the bathroom, 4-5m. Minimal downwards angle. And unfortunately, the first junction it goes into is with the washing machine.
The washing machine outputs bursts of a lot of soapy water, and since there is no preferred direction in the junction (as the kitchen pipe has minimal angle), the water goes both ways - down the drain and up the kitchen pipe, at least half way, and slowly drains from there. Over time, it meets fats in the kitchen drain and forms soapy blocks there, growing in size until eventually blocking the kitchen drain once a year or two.
The proper solution would have been to route the washing machine all the way towards the end of the drain, near the sewer output of the apartment. But lifting the ceramic floor tiles in most of the bathroom doesn't sound like a good idea...
So the attempted solution is to block the washing machine bursts from entering the long kitchen drain pipe. And this is exactly where the backwater valve comes in - but since it's house caliber pipes, there is no kind of valve that can be integrated into the pipe, and I have no place to open the pipe and insert such a valve near the junction box.
And this is why I've built my own.
I've also replaced the sink cover with an easily removable one, so it will be monitored frequently until I see it does its job as expected.