How do I remove this tank sender?

[Sea Change]

I need to gain access inside my diesel tank, and the only possible point of entry is the (defunct) level sensor.
I tried undoing the three machine screws but without resorting to excessive force, couldn't get it to budge.
Does the whole thing unscrew, perhaps?

 

[kingsebi]

It looks like on my tank where it opens by undoing the screws. Don’t you have an inspection hatch?

For the screws: WD40 and prayer?

 

[Sea Change]

It looks like on my tank where it opens by undoing the screws. Don’t you have an inspection hatch?

For the screws: WD40 and prayer?

No inspection hatch. I'd like to add one, but for now I just need access.
I'll apply a bit more brute force...

 

[kingsebi]

You can always drill them out, but then the problem is how to get the remains out of the tank.

 

[Sea Change]

I'm really wanting to avoid having the boat out of commission while I clean swarf from the tank, seeing as I'm currently at anchor.

 

[kingsebi]

Yes, never do that. Don’t ask me how I know.

 

[Sea Change]

I applied the strap wrench... and with zero effort, the sender popped off!
When I last tried removing it, a few weeks ago, it wouldn't budge an inch. Weird. Anyway, good result.

 

[kingsebi]

Great. Well done

 

[johnalison]

It looks like on my tank where it opens by undoing the screws. Don’t you have an inspection hatch?

For the screws: WD40 and prayer?

Not WD40. PlusGas or similar and if necessary leave for a few days. A bit late for the OP but it has worked for me on a similar fitting.