an update for those who care!
a plumber came aorund yesterday and checked things out... turns out the whole wastewater drainage system is fucked, he said some dude with a bigger tool needed to come around today

The shit cleaning gear was so high powered it needed a whole truck to house it! Anyway he had a 20 metre long power drain unclogger thing and said the the blockage was super chronic and shit. Should hopefully be fixed now. Now I dont feel useless for not being able to plunge the thing lol
And thank god I didnt try PD's towel trick!