I live in an apartment and neighbours downstairs complain re my overflow leaking unto their window. Where can it be from and how can it be fixed? Do I need to contact my landlowr/a plumber, or can it be DIYed?
It is not your overflow it's your landlord's overflow.
It should be relatively easy to fix but if you attempt it yourself and mess it up your landlord would be within his rights to charge any repair bill against you.
If you call in a plumber yourself then you will have to pay him unless you have the landlord's agreement to reimburse you.
The people with the problem are your downstairs neighbours - get them to worry the landlord.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix toilets.