Access hole/hatch fitting for fuel tank after discovering diesel bug

[Jam]

Hi
Pumped out all fuel with transfer pump and  filtered it out and in and discarded the stuff nearer to the bottom of tank.  Cut a hole with a 2 blades circular cutter, a hole saw is safer if you can get size as this tool if it sticks can be risky and drill needs 2 hands as can generate a lot of torque off it sticks.  It cut through the plastic tank well and the result was a 112mm hole for cleaning and then fitting the hatch from tek-tanks.  It was very easy and enabled me to clean most of the tank especially just below the fuel pipes.  I added marine 16 as I refilled the tanks.
 

[Moodymike]

Thanks “Jam”. This info is Much appreciated by myself and I’m sure by many others.

[blue-max]

That's very interesting - I have been wanting to  do  something like this for some time (but it seems to  have fallen off the list) Does your tank have baffles and did you  know where they  were located before you chose the spot to  cut. Does the lid seal perfectly - no smells etc? are there different  sizes - I don't have a lot of space.

[Yngmar]

That big rectangular hole on top of the photo is one of the two baffles - they go all the way through and you can store things in them Very obvious where they are on this type of tank.

[blue-max]

Can't recall the rectangular feature  - tank top  seems to be flat - unfortunately no photos to  hand to  check. Anyway bought a hatch  - £25.12 from Wema UK. ( there maybe a discount code) worth a try. Now need to  buy a cutter. Don't fancy using a jig saw. 

[blue-max]

there'e also a  u tube video showing installation

[Ailatan]

Nice brico, very interesting. I add to my to do list

[Jam]

As Yngmar says the tank on my boat, ocean 38, goes back to stern and has sections that you can look down and see the hull below so it’s sectioned up further aft, the whole largest part of tank being the section where the fuel pipe are. I used a camera endoscope thingy, wrong name I am sure, that I had bought a while back from Aldi so could look down the small hole after removing most of fuel via the fuel gauge sender using transfer pump. Allowed me to have a look before cutting the hole. 
Was happy that I did it and can now inspect and clean the largest part of tank directly below the fuel pipes and on shining a torch up toward the sectioned areas it looked pretty clean.  The tank base  sloped down I think towards the fuel pipes.
Be careful as I said using this cutter, it need 2 hands firmly on drill and gently does it.
I also made a fuel polisher (attached) but it blocked hence the need to open and clean the tank, I will use it after a few month and continue with adding marine 16 when I fuel up. 
I know there are differences of opinion regarding fuel polishing but it was pretty cheap to make and can’t run engine in winter for long period as out of water and poor water supply at tap supply