It's probably polyethylene. Here's a list of some manufacturers:
RONCO - one-piece linear polyethylene
TODD โ one-piece polyethylene. Marine tanks.
TRIONIC โ one-piece polyethylene.
ICON TECHNOLGIES (Camping World) โ ABS plastic
Ameri-Kart โ LDPE polyethylene and ABS.
D&M Plastics โ polyethylene
INCA Plastics Molding โ polymer resin
All-Rite โ polyethylene. Makes custom tanks for out-of-business RV companys.
Dura-Cast - polyethylene, Linear Medium Density (LMDPE)
Freeman Engineering - polyethylene
2004 - 2010 Part Timer (35โ 2004 National RV Sea Breeze 8341 - Workhorse)
2010 - 2021 Full Timer (41โ 2001 Newmar Mountain Aire 4095 DP - Cummins)
2021 - ??? Part Timer (31โ 2001 National RV Sea View 8311 - Ford)
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