Sewage problem in my house

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335KB, 752x454px

Hello, /diy/.
I need your advice.
This rough sketch in picrelated depicts a drain system in my house.
Figures 1 and 3 are maintenance pit with a hatch to the main shitpipe leading to the communal system.
Figure 2 point to the water level and a rusted-out hole beneath the maintenance hatch. Shit water doesn't come out of the hole, but the stench.
The only way to repair it is to replace the rusty maintenance hatch piece, but i can't afford it and welding is out of option, as it is completely rusted.

I searched for a provisional solution to keep the stench out of the house - one of my neighbours told me that to filling the maintenance pit with bucket of water would be a good idea.
What do you think about this - it is actually meant to balance the water level and isolate the shit from the air, but wouldn't it just fill the maintenance pit with shit diluted water and eventually push it upwards, filling my basement room with floating turds?