Hi there, new homeowner here. Living in a 60's house in Scotland. Previous owners got a downstairs toilet fitted (only upstairs before). We've had a very slight sewer / damp smell in there since buying, and we're unsure where the problem might lie.

Given the state of the connection of the toilet going into the ground here, part of me thinks it might be this? They didn't tile and seal the connection to the ground. Would we be able to fill this space, or is it worth checking if the toilet needs a wax ring replacement? Without taking the whole toilet off, is there any signs that the wax ring has failed? There seems to be no leaking. The toilet is one of those ones that has very awkward access to the back, as the porcelain goes all the way around the base, so the photos show the only access to the waste pipe.

The smell IMO is worst in the evenings and mornings. It's not awful, but it's just not pleasant in the house. 

We replaced the plug in the sink right next to this, which had a tiny leak. The P-trap was full when we did this, so unlikely that it's letting air through. 

We also found out that the washing machine sometimes gurgles, but taps, showers, and drains run fine. I hear that gurgling can be a sign of a blocked vent stack. There doesn't seem to be any attic access to this, so we'd need to manually inspect from a ladder on the roof.

What would be the best process to start seeing what the problem is? I really can't identify the smell by nose, as when I get close, it's just air + dusty smelling, the smell is more ambient and not direct, so likely a small trickle.

Slight Sewer Smell - Downstairs Bathroom