Gurgling drains – likely cause?

[oyster_plumb]

Thanks both, very helpful. Funnily enough, that seems to be the case. It's not in the attic of a house though, but in a detached garage. Have found the planning for it on the council's database as a garage but nothing that approved it to be converted and rented out privately...

Also no water cylinder, just a small instant water heater

 

[Madrab]

Hmmm ... always best to be careful .. does it have proper smoke detectors, fire safety, electrical certs, did you get a proper tenancy agreement, is he registered, etc Always best to check.

Re the cylinder, I was just wondering what the white tank and the pressure relief valve in the picture were for.

 

[oyster_plumb]

Would anyone know if the ongoing odours could be caused by push fittings not being tight enough? There's still a faint smell but it seems worse after emptying a sink full of hot water... I'm wondering if the hot water is perhaps causing pipes to expand/contract even slightly, which would let out the smell. Is that something that could be happening?

I ask because it seems this place doesn't have planning permission so probably didn't follow building regs either (which might explain why the LL isn't calling anyone out). I'm thinking the foul drainage system is perhaps not up to standard, so might actually be causing these issues. The alternative is that it sounds like a clog, but now I wonder if the quality of the installation further down made that more likely...

It would be helpful to know as I think this might be one for the council after all. Thanks again for everyone's help so far