What are these? Dipsticks? Caps?

I have a new-to-me old septic truck. It is a 1981 Ford L9000 with a CAT 3406B.

On the driver's side of the engine I have found two caps and I can't figure out what they are.

For reference, I have found the oil pan dip stick. It is the yellow one with the handle at the back right of the first picture.

1) What is the blue cap covering? This cap should not be here and I need to get the proper cap or dipstick for this. The blue cap is slightly hidden behind the hose in the middle of the first picture.

2) What is the grey cap (knob) for? It is behind the two hoses in the bottom middle of the first picture.

I looked in the CAT operations manual, but could not figure it out.

DSC09633 by sarrattseptic posted Nov 6, 2021 at 5:16 AM

DSC09640 by sarrattseptic posted Nov 6, 2021 at 5:16 AM

DSC09709 by sarrattseptic posted Nov 6, 2021 at 5:16 AM

DSC09705 by sarrattseptic posted Nov 6, 2021 at 5:16 AM

 

Thank you both for the information.

I am more familiar with smaller engines. This is my first heavy equipment vehicle.

Any good aftermarket parts places for CAT engines?