PVC sheet join together

[Sidid]

I am thinking of PVC floor damp proof membrane sheet for tanking purposes, I.e collecting rainwater for a pond top up purposes on the Allotment, for cheapness, draped across old Anderson shelter sections circled above ground. I want to cut and seal overlaps, normally they seal under pressure clamp and heat, I could try that between two irons etc, has anyone used an adhesive of some sort to join two pieces together.