Existing Drain smells and big mice problem!

I assume visual although I wasn't present so not 100% sure.

 

No as only the utilities area is under the roof and Bathroom under existing house.

The plumbers may of done something fundamentally wrong as initially they even forgot to put a trap for the washing machine and boiler. It was only due to the smells I looked n found them missing.

The traps are installed now but smells still enter the house

 

The bathroom has always been hard to identify as it is always dispersed into the air as it is never as strong at the exit points.

It seems like it disperses a build up and then lingers or the exit point is not visible...

The utilities on the other hand I am pretty sure its coming from behind the washing machine and boiler.
Previously I have removed the washing machine and have noticed it far stronger from the gaps between the wall and floor tiles and through the waste pipe...

 

This morning we woke up with a very stale smell in the kitchen/diner which lingered throughout the ground floor.
The smell was very strong from behind the washing machine and the area where the 2 tiles have been lifted (definitely more stronger putting nose between worktop and washing machine).

This smell thought was stale but not eggy like other occasions.

I called the builder but he only came an hour later and by then the smells had weakened and we had the washing machine on as well so the smell between worktop/washing machine was of washing smells.

The builder said he is pretty sure its not the old drain as according to him and a few people he has asked, the fact we have lifted up 2 tiles there should be a consistent strong smell from the old drains which there isn't.
There is a stale smell when you put your nose down into the whole but no where strong to stink the whole room...

Although his conclusion is that he believes it is nothing to do with the old drain and rather the bathroom sink, shower or toilet, is there anything I can advise him to do to make sure or does he have a valid point with regards to the old drain system?

 

He has built over, not sure exactly why and will need to ask him but from asking a few other builders it seems a common practice to leave them there as it is more of hassle/bigger job to dig them all out.

Well I believe there are not filters but we have had the smell since day one of installing the brand new washing machine....
Although the smell is more strong from behind the washing machine, the smell used to be just as bad under the boiler before they used the expanding foam to cover up the gap in the floor....

 

New pipe run

 

We are thinking of getting a CCTV drain test which includes testing of traps, using dyes and smoke bomb test as well.
Do any of you think this would be a wise move and roughly how much would it cost?

 

I wasn't present but I am guessing a quick look if even that

 

Any guides on how to use these?

 

How do I access the drain though? Through the manhole?
I have no idea about anything drain related...