Volvo FM water/coolant tank

Currently using a day cab Volvo FM (out based from the yard - so no one around to ask) -

Checked it today and level is fine but how the bloody hell are you supposed to fill it.

There is a gap of about 4/5 inches from the cap of the tank to the top of the compartment.

Looked all over the rear of the cab and elsewhere under the bonnet and nothing obvious

No manual knocking around either.

Can someone please enlighten me?

The cab needs to be tilted. I understand that Volvo designed it that way to prevent drivers from topping up with water, rather than the correct coolant.

Another useful design feature from Volvo. The FL10 was the same.

Sent while having a beer

Cheers.