DooFlex Pillow Type PVC Water Tanks ( Water Bladder) are normally â pillowâ shaped tanks having a low profile, made from heavy duty/ special application PVC/ TPU coating fabric, which gives high abrasion and UV resistance. PVC water tanks are used for temporary or long-term water or liquid storage of oil, potable water, sewage, rainwater chemical spillage waste and other liquids. Pillow pvc water tanks are very lightweight, reliable, quick and simple.