[toga]

Does anyone know the type of plastic on the following tanks?

I have two tanks with cracks from a 1978 airstream soveriegn 31 ft CB as follows.
Water Tank
INCA 562
T1237 600833
and
Sewer Tank
INCA H323
T1244 600843
imp gal 18.32
What type of plastic are these? Polyethylene? Is there only one type of polyethylene. My welder says it has to be the same rod type.

Pictures attached.

Thanks,

John