How are socket,nipple fittings fastened onto tank.They need to do this in a airtight controlled ventilated room, venting outside. Employees will accumulate toxic plastic fumes in their bodies and get sick over time.This is rotational moulded polyethylene which is a vastly higher quality finished product than injection or blow moulding. The slow cooked polymer will last for years without cracking or going brittle even after long time in direct sunlight. Do not laugh. This is best way to make water tanks.