Toilet dont get clog if users dont throw non bio degradeable things to flush. My toilet 12 years, no such issues.

Are you sure you want to DIY ? Ask a plumber and if he finds some solid stuff, bill the tenant. Otherwise you bear the cost.

If is a highrise, it could be the common discharge pipe outside your unit.

Safe to leave it overnight?
Ok, will try.
My house where i am leaving is also ok after 8 years.

I thought of asking the hardware shop first for their advise because according to my tenant, it is sometimes only now. It is a new tenant, just 2 weeks.

I wont be surprise if the previous tenant threw things inside, it was a problematic tenant.

Common discharge pipe is one for all bathrooms? Other bathrooms no complain so far.

I think siphonic design is more prone to such issues compared to wash down toilets due to the narrower outlet.
I'm just guessing only it is Rm200, i have no idea. 

Yes, definitely will go to the hardware shop first, the uncle there gives good advice and what to use. If it doesn't work, then i will resort to a plumber.

It's a new tenant, 2 weeks only. I'm am not surprised if the previous problematic tenant threw things in there.

Yup, 1 try and then plumber. Won't drag too long.
Yup, DIY first and if can't, straight get the plumber.

Yea, was kind of troublesome tenant, doesn't take care of some things and always call me for repairs. When ask how it happened, can't answer